The importance of physical fitness in the performance of adequate cardiopulmonary resuscitation

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DOI 10.1378/chest.115.1.1581999;115;158-164Chest

Carvajal, Antonio J. lvarez and Jos L. Chicharro

Alejandro Luca, Jos F. de las Heras, Margarita Prez, Juan C. Elvira, Alfredo

*ResuscitationPerformance of Adequate CardiopulmonaryThe Importance of Physical Fitness In the

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The Importance of Physical Fitness Inthe Performance of Adequate

Cardiopulmonary Resuscitation*Alejandro Luca, MD, PhD; Jose F. de las Heras, MD;Margarita Perez, MD, PhD; Juan C. Elvira, MD; Alfredo Carvajal;Antonio J. Alvarez, MD; and Jose L. Chicharro, MD, PhD

The aim of the present investigation was to evaluate the influence of the physical fitness of acardiopulmonary resuscitation (CPR) provider on the performance of and physiologic response toCPR. To this end, comparisons were made of sedentary and physically active subjects in terms ofCPR performance and physiologic variables. Two study groups were established: group P(n 14), composed of sedentary, professional CPR rescuers (mean [ SD]; age, 34 6 years;

VO2max, 32.5 5.5 mL/kg/min), and group Ex (n 14), composed of physically active, nonexpe-rienced subjects (age, 34 6 years; VO2max, 44.5 8.5 mL/kg/min). Each subject was requiredto perform an 18-min CPR session, which involved manual external cardiac compressions (ECCs)on an electronic teaching mannequin following accepted standard CPR guidelines. Subjects gasexchange parameters and heart rates (HRs) were monitored throughout the trial. Variablesindicating the adequacy of the ECCs (ECC depth and the percentage of incorrect compressionsand hand placements) also were determined. Overall CPR performance was similar in bothgroups. The indicators of ECC adequacy fell within accepted limits (ie, an ECC depth between 38and 51 mm). However, fatigue prevented four subjects from group P from completing the trial.In contrast, the physiologic responses to CPR differed between groups. The indicators of theintensity of effort during the trial, such as HR or percentage of maximum oxygen uptake (VO2max)

were higher in group P subjects than group Ex subjects, respectively (HRs at the end of the trial,139 22 vs 115 17 beats/min, p < 0.01; percentage of VO2max after 12 min of CPR,46.7 9.7% vs 37.2 10.4%, p < 0.05). These results suggest that a certain level of physical

fitness may be beneficial to CPR providers to ensure the adequacy of chest compressionsperformed during relatively long periods of cardiac arrest. (CHEST 1999; 115:158164)

Key words: cardiopulmonary resuscitation; exercise; fitness.

Abbreviations: CPR cardiopulmonary resuscitation; ECC external cardiac compression; HR heart rate;RER respiratory exchange rate; Ve minute ventilation; Vo

2 oxygen uptake; Vo

2maxmaximum oxygen uptake;

Vt tidal volume

To date, the early performance of adequate chest(cardiac) compressions is a standard of care that

is considered to provide the optimal outcome incardiopulmonary arrest.1 Manual external cardiaccompressions (ECCs) represent a simple and readily

available cardiopulmonary resuscitation (CPR) tech-nique that artificially produces sufficient cardiacoutput to maintain basal cardiac and neurologicactivities until spontaneous circulation is restored bymethods such as mechanical ventilation, defibrilla-tion, or drug administration.2,3 However, despite itsproven efficacy, manual ECC has disadvantages. Forexample, it is difficult for one person to delivervigorous, manual ECCs for long periods, which

*From the Departamento de Ciencias Morfologicas y Fisiologa,Universidad Europea de Madrid (Drs. Luca and Perez); Servi-cio Especial de Urgencias 061, Insalud, Madrid (Drs. de lasHeras, Elvira, and Alvarez); and Universidad Complutense deMadrid (Dr. Chicharro); Spain.

This study was partially funded by Tecnicas Medicas M.A.B.(Barcelona, Spain).Manuscript received April 7, 1998; revision accepted July 13, 1998.Correspondence to: Alejandro Luca, MD, PhD, Unidad deInvestigacion, Escuela de Medicina de la Educacion Fsica y elDeporte, Facultad de Medicina, Pabellon VI, 5a Planta, Univer-sidad Complutense de Madrid, 28040 Madrid, Spain

clinical investigations in critical care

158 Clinical Investigations in Critical Care

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results in inadequate chest compressions that may beinsufficient to provide the blood flow required tomaintain critical organ function.4 Several authorshave reported different methods to improve basicCPR (eg, variation of compression rate and abdom-inal binding).3,5,6 Furthermore, mechanical activecompression-decompression CPR has been intro-duced in an attempt to improve the outcome of CPR

after cardiac arrest.7

Little attention, however, hasbeen focused on the fact that the fatigue of the CPRprovider may result in inadequate compression.8

On the other hand, numerous epidemiologic sur-veys suggest that adequate, regular exercise canmaintain or improve fitness, preserve good health,and enhance the quality of life in comparison to amore sedentary style of life.9 Moreover, a number ofstudies have reported a potentially beneficial rela-tionship between regular physical activity and severalindicators of productivity in physically active employ-ees.10 Consequently, it may be hypothesized that ahigh level of physical fitness could improve the

efficacy of CPR. Although the data with which toevaluate the energetic cost of CPR are scarce,previous research suggests that such a procedure isphysiologically demanding on subjects, includingwell-trained professionals. Indeed, blood lactate con-centrations of approximately 3.0 mmol/L and heartrates (HRs) of approximately 130 beats/min havebeen reported recently in experienced professionalCPR rescuers after a 30-min session of standardCPR.11

The aim of the present investigation was to eval-uate the influence of the CPR providers physicalfitness on performance and physiologic variables

during the CPR session. A comparison was made ofthe results obtained from two subject groups: seden-tary, professional CPR rescuers; and physically ac-tive, nonexperienced subjects.

Materials and Methods

Subjects

Fourteen experienced, male, professional CPR rescuers (groupP) from a mobile intensive care unit (Servicio Especial deUrgencias 061, Insalud, Madrid, Spain) with a mean ( SD) of6 2 years of experience (range, 2 to 11 years), and 14 male

health professionals (physicians, physical therapists, and exercisephysiologists) with no previous experience in CPR (group Ex)were selected as subjects for the study. The subjects in group Pwere sedentary and had not performed any regular, vigorousexercise during the preceding 2 years. In contrast, group Exsubjects were physically active and had followed an exerciseprogram (3 to 5 sessions/wk, each consisting of 20 to 60 min ofcontinuous activity such as running, cycling, or swimming) similarto that recommended by the American College of Sports Medi-cine to improve and maintain cardiorespiratory fitness in healthyadults.12

The mean ( SD) age, height, and weight, respectively, of thesubjects were as follows: group P, 34 6 years, 171.7 5.7 cm,and 80.4 13.3 kg; group Ex, 34 6 years, 176.3 4.7 cm, and77.3 10.8 kg. Written informed consent was given prior toparticipation in the study in accordance with the institutions(Escuela de Medicina del Deporte, Universidad Complutense deMadrid, Spain) guidelines for human subjects. Group Ex subjectsreceived a brief training course in CPR prior to the trial.

Maximal Exercise Test

Before the initiation of the study protocol, all subjects per-formed an incremental exercise test to exhaustion to determinemaximum oxygen uptake (Vo2max) and ventilatory threshold(Vt) using an automated breath-by-breath system (CPX; MedicalGraphics; St. Paul, MN). The exercise test was performed on acycle ergometer (Ergoline 900; Ergo-line; Barcelona, Spain) andconsisted of a ramp protocol starting at 0 W. The workload wasincreased by 25 W/min, and the pedal frequency was keptconstant at 60 to 80 revolutions/min. All exercise tests wereterminated voluntarily by the subjects or when the establishedtest termination criteria had been met.13 Vt was determinedusing the criterion of an increase in both the ventilatory equiva-lent for oxygen and the end-tidal Po2 with no increase in theventilatory equivalent for carbon dioxide.14

CPR Performance

Each of the subjects performed a standard CPR session on anelectronic CPR teaching mannequin (Ambu Man-C; Ambu In-ternational; Copenhagen, Denmark). CPR included only manualECCs since no ventilation was provided by the subjects. ECCswere conducted according to the following accepted guidelines:(1) subjects kneeled beside the mannequin; (2) a rate of 80 to 100compressions/min was maintained; (3) a depth of 38 to 51 mmwas maintained; and (4) a compression duration of 50% of thetotal compression cycle or duty cycle, which includes both thephases of chest compression and passive decompression of thechest wall, was maintained.15,16 Criteria for the termination ofresuscitation were defined as the subjects physical limit (physical

exhaustion or pain) or 18 min of resuscitation.The mannequin was equipped with a real-time remote display

that recorded the total number of compressions and the numberof correct compressions. Compressions were recorded as correctif both depth and hand placement were in keeping with standardadvanced cardiac life support guidelines.15

A specially designed computer program (AmbuCPR; Ambu;Glostrup, Denmark) recorded each CPR session as a graphic,semiquantitative plot of compression depth vs time. The averagevalues of the following variables were obtained from the manne-quin after 6, 12, and 18 min of CPR: compression rate (ECCs/min); compression depth (mm); and compression adequacy,which was recorded as the percentage of complete cycles (com-pression duration of 50% of duty cycle) and as the percentageof incorrect hand placements. Subjects were not permitted to

watch the computer monitor during performance. After comple-tion of the test, each subject was informed about their ownperformance. They were instructed not to inform or share theirexperience with their peers.

Physiologic Variables During CPR

Subjects wore a mouthpiece connected to a small, lightweight(26 g) pneumotachograph (Prevent; Medical Graphics; St. Paul,MN) for the duration of the CPR session. A pneumotacographenhances subject comfort by eliminating the need for cumber-

CHEST / 115 / 1 / JANUARY, 1999 159



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some breathing valves and hoses, and heavy headgear. Expiredair was analyzed by an automated breath-by-breath system (CPX;Medical Graphics) in order to monitor gas exchange data contin-uously during each CPR session. Before each trial, the instru-ments were calibrated using a standard 3-L syringe and precisionreference gases. Corrections were made for barometric pressure,ambient temperature, and humidity. HR (beats/min) was contin-uously monitored during the sessions as a modified 12-leadelectrocardiographic tracing (EK56; Hellige; Freiburg, Germa-ny). The 60-s average of the following physiologic parameters,

monitored during the CPR session at 6, 12, and 18 min weredetermined: HR (beats/min); oxygen uptake (Vo2) in absoluteand relative units, respectively (L/min and mL/kg/min); minuteventilation (Ve; L/min); and respiratory exchange ratio (RER). Inaddition, the percentage Vo2max at 6, 12 and 18 min ofresuscitation was also determined.

Capillary blood samples (50 L) were taken from fingertipsbefore and immediately after the termination of each session todetermine blood lactate levels (mmol/L) using an automatedlactate analyzer (YSI 23 L; Yellow Springs Instruments; YellowSprings, OH).

Statistical Analysis

Data were analyzed using the SPSS 7.5 for Windows statistical

package (SPSS Inc.; Chicago, IL). The Kolmogorov-Smirnovtest17 was used to demonstrate a Gaussian distribution of data. AStudents t test for unpaired data was used to compare physio-logic variables between groups during the exercise test. Bloodlactate levels were compared within and between groups using aStudents t test for paired and unpaired data, respectively. Inaddition, the following comparisons of average physiologic andperformance variables during the CPR session were performed:within groups at 6, 12, and 18 min using one-way repeated-measures analysis of variance; and between groups at 6, 12, and18 min using one-way analysis of variance. When a significant Fratio was found, a Newman-Keuls post hoc analysis was per-formed to determine where the significant differences existed. Anonparametric test (Mann-Whitney) was used for data that didnot show a normal distribution. The level of significance was setat 0.05. All data are expressed as the mean ( SD).

Results

Maximal Exercise Test

Physiologic data obtained in the maximal exercisetest are shown in Table 1. Subjects in group Exshowed higher maximal and Vt values than those ingroup P.

CPR Performance

CPR Duration and Subject Assessment: There wasno significant difference in the duration of CPR be-tween groups, although a tendency toward a longerduration was observed in group Ex vs group P, respec-tively (1,080 0 vs 979 178 s). All the subjects ingroup Ex were able to complete the 18-min CPRsession, whereas four subjects in group P stopped thesession before 18 min. Reasons for early terminationwere pain in the upper extremity or in the vertebralcolumn (n 2) and dyspnea (n 2). Consequently,

the statistical comparison between groups at 18 minincluded only 10 subjects from group P.

Compression Rate: All the subjects were able tomaintain an ECC rate of 80 to 100 compressions/min, which is in agreement with accepted guidelinesfor standard CPR.15,16

Compression Depth: No significant differenceswere found within groups during the trials (p 0.05;Fig 1). Although average values were consistentlylower in group Ex subjects throughout the tests(p 0.001, p 0.01, and p 0.05 at 6, 12, and 18min, respectively), the mean values fell within stan-dard accepted limits (38 to 51 mm) in both groups.

Percentage of Incorrect Compression Cycles: Nosignificant differences within or between groupswere found (Fig 1).

Percentage of Incorrect Hand Placements: Nosignificant differences within or between groupswere found (Fig 1).

Physiologic Variables During CPR

Lactate Levels: Lactate levels significantly in-creased (p 0.001) within the groups after CPR.There were no significant differences in pre-andpost-CPR lactate levels between groups (Fig 2).

HR: Although the average values did not change in

group Ex during the trial, the average HR increasedin group P (p 0.01) at 12 and 18 min during CPRwith respect to values at 6 min (Fig 3). However, HRvalues were significantly lower in group Ex(p 0.01) at each follow-up time.

Ventilation: No significant differences within orbetween groups were observed (Fig 3).

RER: In both groups, RER values were lower

Table 1Maximal Exercise Test*

Group Ex,n 14

Group P,n 14 p Value

Maximal valuesVo2max, L/min 3.4 0.6 2.6 0.4 p 0.001Vo2 max, mL/kg/min 44.5 8.5 32.5 5.5 p 0.001Ve, L/min 144.0 34.7 110.8 25.2 p 0.001HR, beats/min 183 10 181 12 NS

Values at Vt

Vo2, L/min 1.9 0.4 1.4 0.2 p 0.001Ve, L/min 43.97 9.7 34.6 5.7 p 0.001HR, beats/min 131 11 123 11 NS

*All values are expressed as mean ( SD).NS no significant difference.




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during the second part of the CPR session (p 0.05for 12 and 18 min vs 6 min; Fig 3). No significantdifferences between groups were detected.

V O2: No significant differences were found withingroups during the trial whether Vo

2was expressed in

absolute or relative units (Fig 4). No significantdifferences were encountered between groups withthe exception of higher Vo2 in group Ex than ingroup P at 18 min (p 0.05).

Percentage of V O2max: There were no significant

differences within groups (Fig 4). However, group Psubjects tended to perform CPR at a higher percent-age of Vo

2max than group Ex subjects. This was

statistically significant at 12 min (p 0.05).

Discussion

The main finding of this study was that, despitetheir lack of expertise, nonexperienced, physically fitsubjects showed different physiologic responses thanand comparable CPR performances to professional,sedentary subjects. The average values of CPR per-formance indicators such as the percentages of in-correct cycles and incorrect hand placements weresimilar in both groups. In addition, although ECC

depth was consistently lower in group Ex at eachfollow-up time, the average value was still withinstandard accepted limits (38 to 51 mm).15,16 Further-more, the duration of the trials tended to be longerin group Ex. In group Ex, each subject was able tocomplete the trial, whereas 4 of 14 experiencedrescuers in group P showed signs of physical fatiguethat forced them to stop ECCs before 18 min. Itshould be noted that in real situations a minimum of30 min of CPR is often required.15,16 Moreover,since hypothermia confers protection against theeffects of hypoxia, resuscitation efforts in hypother-mic patients should be continued for much longer.16

The physiologic responses of the subjects dif-fered considerably between groups. Group P sub-jects showed significantly higher HR valuesthroughout the trial and also showed a tendency toprovide compressions at a higher percentage ofVo2max. These observations suggest that physicalfitness has a significant effect on the physiologicresponse of resuscitation providers. Physically fitindividuals can provide ECCs at a lower intensityof exercise and, therefore, have a higher resistanceto fatigue. Absolute Vo

2tended to be lower in

group P, perhaps suggesting a greater economy ofmovement during the resuscitation maneuvers,which in turn may be attributed to previousexperience (5 3 years). Alternatively, these find-ings simply may be attributed to the fact thatvalues of Vo2max were considerably lower ingroup P. However, it should be kept in mind thatthese subjects performed ECCs at a higher per-centage of Vo2max (ie, at a higher intensity ofeffort). Finally, blood lactate levels significantlyincreased in both groups after CPR, but no signif-

Figure 1. ECC adequacy: compression depth, percentage ofincorrect cycles, and percentage of incorrect hand placements. p 0.001, p 0.01, and p 0.05 for group Ex vs group P at6, 12, and 18 min, respectively.

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icant differences were found between groups. Thismay be related to the fact that the majority ofgroup Ex subjects had undergone exercise thatmainly involved the lower extremities (walking,running, cycling, etc.), whereas ECC principallyinvolves the trunk and upper body muscles.

Despite the tendency of previous resuscitationresearch to focus on advanced life support mea-sures, the provision of adequate ECCs is still thestandard care procedure for victims of cardiacarrest.8 In this regard, the present study has

evaluated the effects of aerobic training on severalindicators of ECC performance (such as the res-cuers time to fatigue and the adequacy of com-pressions) and on the physiologic responses tosuch activity. Although other authors have re-ported the physiologic responses of experienced,professional CPR rescuers (a mean Vo2max ofapproximately 45 mL/kg/min) to a session of stan-dard CPR that lasted approximately 30 min, nodata concerning their aerobic training was provid-ed.11 In the present investigation, a group ofphysically active individuals with relatively highVo2max values (approximately 45 mL/kg/min), incomparison with standard values for healthy adultsof the same age group (30 to 39 years),18 wasselected. In contrast, the Vo2max of group Psubjects was moderate and was considerably lower(approximately 32 mL/kg/min) than that of groupEx subjects. This contrast permitted evaluation ofthe influence of physical fitness on the physiologicresponses of CPR providers.

The present findings are in agreement with the

suggestions of Baubin et al11 and show the needfor at least a minimum level of physical condition-ing in CPR providers. Such a conclusion is sup-ported by the fact that physically fit individualswith no previous experience in resuscitation ma-neuvers were as effective as sedentary, profes-sional rescuers in performing chest compressions.The practice of ECC is a moderately intenseactivity that requires a certain level of physicalfitness, as shown by the increase in blood lactatelevels in both subject groups. Furthermore, the

metabolic cost of CPR was not negligible (a Vo2 ofapproximately 14 mL/kg/min, or 4 metabolicequivalents, in group P) and corresponds to that ofactivities such as recreational cycling or swimming.These are commonly perceived as moderatelyintense by healthy adults.19 In addition, duringsituations of actual cardiac arrest, ECCs shouldnot be interrupted at all during resuscitation sincecardiac output increases cumulatively during thefirst compressions.20 Other authors also have sug-gested that there is little margin of error in theprovision of adequate critical organ perfusion byECC.2123 Furthermore, it has been reported re-cently that trained personnel reach a state ofphysical fatigue relatively rapidly, at which timethe compressions probably become inadequate toensure vital organ perfusion.8 Moreover, CPRproviders might not be able to recognize their ownfatigue or its effects on ECC performance.3,8

On the other hand, the limits of this investigationinclude the fact that CPR was performed on amannequin under almost ideal laboratory conditions.

Figure 2. Blood lactate levels. * p 0.001 in both groups for pre- vs post-CPR.




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Under real conditions (ie, during an actual arrest),rescuers probably achieve better ECC performancebecause chest compressions are easier to perform inhuman beings and there is a sense of urgency.8

In conclusion, the findings of this study suggestthe possibility of including a fitness program (ie, lightto moderate aerobic exercise) for CPR providers aspart of their general training. On the other hand,

CPR training is not limited to paramedic personnel.In fact, in Western societies, the survival rate ofvictims of cardiac arrest largely depends on theintervention of trained bystanders in initiating andmaintaining CPR before paramedic personnelarrive.24 The fact that nonexperienced, physically fitsubjects and professional, sedentary subjects showedcomparable CPR performances, despite contrasting

Figure 3. Physiologic responses during ECC: HR, Ve, and RER.* p 0.01 for 12 and 18 min vs 6 min in group P; p 0.01 for group Ex vs group P; and ** p 0.05 for 12and 18 min vs 6 min.

Figure 4. Physiologic responses during ECC: Vo2 and effortintensity (percentage of Vo2max). group Ex vs group P at 18min, p 0.05; and group Ex vs group P at 12 min, p 0.05.

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physiologic responses, strengthens the notion thatphysical fitness can have a positive impact on resus-citation efforts.

ACKNOWLEDGMENT: The authors are grateful to TecnicasMedicas M.A.B. (Barcelona, Spain) for provision of laboratorymaterial and to Ana Burton for her linguistic assistance.

References

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3 Ward KR, Menegazzi JJ, Zelenak RR, et al. A comparison ofchest compression between mechanical and manual CPR bymonitoring end-tidal Pco2 during human cardiac arrest. AnnEmerg Med 1993; 22:669 674

4 Paradis NA, Martin GB, Rivers EP, et al. Coronary perfusionpressure and the return of spontaneous circulation in humanCPR. J Am Med Assoc 1990; 263:11061113

5 Wik L, Naess PA, Ilebekk A, et al. Simultaneous activecompression decompression and abdominal binding increasecarotid blood flow additively during cardiopulmonary resus-citation (CPR) in pigs. Resuscitation 1994; 28:5564

6 Tucker KJ, Khan J, Idris A, et al. The biphasic mechanism ofblood flow during CPR: a physiologic comparison of activecompression-decompression and high-impulse manual exter-nal cardiac massage. Ann Emerg Med 1994; 1994:24:895906

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9 Bouchard C, Shephard RJ, Stephens T. Physical activity,fitness, and health. International proceedings and consensusstatement. Champaign, IL: Human Kinetics Publishers, 1994

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changes in fitness and lifestyle upon health care utilization.Can J Public Health 1983; 74:5154

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for exercise testing and prescription. 6th ed. Malvern, PA:Lea & Febiger, 1986; 9596

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DOI 10.1378/chest.115.1.1581999;115; 158-164Chest

Carvajal, Antonio J. lvarez and Jos L. ChicharroAlejandro Luca, Jos F. de las Heras, Margarita Prez, Juan C. Elvira, Alfredo

*Cardiopulmonary ResuscitationThe Importance of Physical Fitness In the Performance of Adequate

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The importance of physical fitness in the performance of adequate cardiopulmonary resuscitation

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