Maturitar, 10 (1988) 65-69 Elsevier Scientific Publishers Ireland Ltd.

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MAT00467

Case Report

Respiratory changes during flush

a menopausal hot

AS. Kindlen and R.E.C. Munro

L@artment of Science, Queen Margaret College, Edinburgh, Scotland, U.K.

(Received 11 August 1987; revision received 30 December 1987; accepted 9 February 1988)

The effect of a menopausal hot flush on respiratory parameters was studied in one subject on nine separate occasions. The flushes were associated with a significant increase in the production of carbon dioxide and lesser but still significant changes in oxygen consumption, tidal volume and minute volume. The changes in respiratory frequency and respiratory quotient were not significant. Significant changes in carbon dioxide production and oxygen consumption were still evident well into the climacteric.

(Key words: Menopause, Hot flush, Respiratory changes, Physiological changes)

Introduction

The symptoms reported by women during the climacteric vary considerably, but hot flushes are widely experienced and cause discomfort and even distress in many cases [l]. Surprisingly little scientific investigation has been focused on the flush itself [2,3], perhaps because of the unpredictable timing and the difficulty of provoking flushes under laboratory conditions. Little information, other than anecdotal (41, is available on the variability of the flush between subjects, within one subject or with the passage of time.

In this investigation, the changes in the volume of inspired air and the volume and composition of expired air, before, during and after a flush, were studied using a Morgan Exercise Test System.

Method

One woman (aged 54 yr), engaged in a long-term study of her own basal metabolic rate, was the subject of this study. The methodology was therefore

Correspondence to: A.S. Kindlen, Dept. of Science and Dietetics, Queen Margaret College, Edinburgh, Scotland, U.K.

typical of one used in the assessment of basal metabolic rate, with estimations carried out daily.

The woman fasted for 10 h (overnight) and immediately prior to the start of the estimation rested for. 30 min in a comfortable prone position, wearing light clothing. During the estimation, the same comfortable position was maintained and the subject used a cassette tape player fitted with headphones to exclude external noise and, as far as possible, minimize her concentration on her own breathing. The ambient temperature was maintained at 20-22OC.

The Morgan Exercise Test System continuously measures the volume of inspired air using a pneumotachygraphic system and computes the volume of expired air. The oxygen and carbon dioxide concentrations in the expired air are measured, the oxygen by the paramagnetic method and the carbon dioxide by infrared. A minute-by-minute record over 16 min is obtained of minute volume, respiratory frequency, average tidal volume, oxygen consumption, carbon dioxide production and respiratory quotient. The 16-minute cycle is then repeated.

In the investigation, two 16-min cycles were recorded, with a short rest period between cycles. The results‘for the first 3 min in each cycle were discarded - this period of time allowed any atmospheric air in the analyzers to be flushed out. During those cycles in which a flush occurred, the minute was noted in which the subjective sensation of the flush began. Any flush beginning within the first 3 min of a cycle was discarded.

Extensive calibration studies of the instrument used have shown that it is necessary to take into account the performance of the pneumotachigraph at low air flow rates. A small error may be introduced in the selection of a calibration factor for these conditions. However, once the factor is established, the effect of the error becomes constant under such standardized conditions. An analysis of variance has shown that there was no significant difference between means of groups of 10 vol. measurements made with a constant calibration factor, on 3 separate days, using 2 operators (F = 2.66, P = 0.087). For this reason, all results have been expressed as percentage increases rather than absolute values.

Results

The duration of the flush was difficult to determine [1,4], but the subjective effect appeared, to last for approximately 3 min. These 3 min were therefore compared with the 10 non-flush min in the same cycle. The results for volume of &bon dioxide produced, oxygen consumed, average tidal volume, respiratory frequency, minute volume and respiratory quotient were expressed as the mean percentage increase f standard error of the mean (S.E.M.) in relation to the resting value (see Table I).

When all 27 flush min were compared with the 90 non-flush min over the 9 cycles using Student’s i-test, the increases in carbon dioxide production of 9.2% (P < O.OOl), in oxygen consumption of 7.3% (P < 0.001) and in minute volume of 6.9% (P < 0.001) were found to be highly significant. The effect of flushing on the average tidal volume was also examined but found to be much less

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TABLE I

CHANGES IN RESPIRATORY PARAMETERS DURING MENOPAUSAL HOT FLUSHES

Mean% increase f S.E.M.

df P Range of

= 115) values for all flush and non-flush minutes

ClUbOIl dioxide production

&Ywn consumption

Respiratory quotient

Tidal volume

Respiratory frequency

Minute volume

9.2 f 2.3 5.31 < 0.001 115-170 ml/TV

7.3 f 2.4 4.07 < 0.001 W-220 ml/TV

1.7 f 1.2 1.13 NS 0.63-0.93

5.1 f 1.9 2.82 = 0.003 288-463 ml

1.89 f 2.39 0.71 NS 11-18/min

6.9 f 1.56 5.11 < 0.001 4.5-6.21

significant. The effect on respiratory frequency and respiratory quotient was not significant (see Table I). Although individual respiratory values must be treated with caution, because of their intrinsically variable nature, the following observations can be made.

The peak value for carbon dioxide production in 5 out of 9 cycles occurred within the 3 flush min and in four instances in the 2 min immediately preceding the sensation. The peak value for oxygen consumption in 7 out of 9 cycles occurred within the 3 flush min and in one case in the 2 min preceding the sensation. In the ninth cycle the peak oxygen consumption occurred in the 2 min preceding the flush sensation, but since this came within the first 3 min of the cycle this observation was discarded. The peak value for minute volume in 8 out of 9 cycles occurred during the flush minutes, and in one cycle in the preceding 2 min. The peak values for tidal volume and respiratory frequency were not clearly related to the flush minutes.

Discussion

The results obtained show a significant increase of 9.2% in carbon dioxide production and a smaller but also significant increase of 7.3% in oxygen consumption reflected in the significant change in minute volume over the 3 flush min. The increase in oxygen consumption compares with the 5-l 5% increase which can be inferred from studies on basal metabolic rate [5,6]. It is notable that, although the changes in carbon dioxide production and in oxygen

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consumption were each highly significant, both the value of the percentage increase and the order of significance of the increase in carbon dioxide production were considerably greater than those for oxygen consumption.

The times at which changes took place, i.e. the positions of the peak values, are of interest. It might be expected that the sensation of warmth or discomfort would give rise to increased ventilation, but it should be noted that in about one- third of the cases the change in carbon dioxide production preceded the sensation, suggesting that it may be part of the primary disturbance involving the hypothalamic thermoregulatory area [7], rather than a response to a peripheral effect.

The position of the peak values therefore suggests that the respiratory changes take place at the same time as, or just before, the flushing sensation. It is of interest to compare these findings with those reported by Molnar [3] and Tataryn 171. Molnar’s single subject showed physiological changes which preceded the ‘sensation’, while in Tataryn’s study the physiological changes came after the ‘sen- sation’.

The correlation between the subjective sensation and the physiological changes is confused in the literature [l], possibly because there appear to be two different subjective sensations which have not been clearly separated.

The first could be described as a premonition, such as that referred to in Sturdee’s study [8] as an “indefinable sensation of an impending flush”, just before the onset. The sensation mentioned in Tataryn’s study also appears to fall into this category. His subjects experienced a sensation, which was difficult to describe, that caused them to signal an attack. However, this sensation was “quite divorced from the later feeling of flushing and sweating”.

The second subjective sensation is the sudden feeling of heat, felt mainly in the face and neck, which is probably the sensation mentioned by Molnar and commonly described by women as a flush. Some of the confusion may arise from the fact that the early sensation is not consciously perceived by all of the subjects. Our subject experienced a premonition in the form of a slight feeling of nausea only when the flush occurred during a period of physical activity. This may suggest that, in her case, conscious perception of the premonition is only achieved when it occurs during a period of increased cortical arousal and increased sympathetic activity typical of physical activity.

Silverman [9] recorded an initial fall in skin temperature, indicating cutaneous vasoconstriction, “after the subjective sensation”. This presumably occurred after the premonition, since it preceded the rise in skin temperature, indicating the vasodilator flushing effect. This vasoconstriction may be part of more widespread sympathetic activity giving rise, in our subject, to a feeling of nausea.

Molnar has further shown that transient physiological changes take place in about 30% of episodes without any subjective sensation of the flush [lo]. The normal variability of respiratory values would make this difficult to identify with our method, but the effect may still be significant.

The original investigation was carried out in 1984. However, since flushes are still being experienced by our subject, who is now 8 yr into the climacteric, we

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have recently carried out further investigations to try to record changes in respiratory values during a flush, for comparison with the earlier results.

Unfortunately, only two measurement cycles have included a flush, but a significant increase in carbon dioxide production was recorded, with a mean increase of 5.6% f 1.5 (t = 2.68, df = 24, P = 0.007), as well as a significant increase in oxygen consumption of 4.2% f 2.6 (t = 1.77, df = 24, P = 0.045). From these two cycles, it would appear that, while the magnitude of the flush effect had diminished over the 3 yr, the effect was still significant. Moreover, as in the original results, the change in the carbon dioxide production and its level of significance were greater than those for oxygen consumption.

The results indicate that the occurrence of overt flush episodes, even at a well- advanced stage in the climacteric, have a significant effect on respiratory parameters and it is conceivable that even a sub-threshold flush might have some effect.

Acknowledgements

We wish to thank Mr. D. Sutherland, Department of Science, Queen Margaret College, for his statistical advice.

References

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Tulandi T, Lal S. Menopausal hot flush. Obstet Gynecol Surv 1985; 40: 553-563. Sturdee DW, Reece BL. Thermography of menopausal hot flushes. Maturitas 1979; 1: 201-205. Molnar GW. Body temperatures during menopausal hot flushes. J Appl Physiol 1975; 38: 499- 503. Voda AM. Climacteric hot flash. Maturitas 1981; 3: 73-90. Collett ME. Basal metabolism at the menopause. J Appl Physiol 1949; 1: 629-636. Hafkesbring R, Collett ME. Day to day variations in basal metabolism of women. Am J Physiol 1924; 70: 73-85. Tataryn IV, Lomax P, Bajorek JG, Chesarek W, Meldrum DR, Judd HL. Postmenopausal hot flushes: a disorder of thermoregulation. Maturitas 1980; 2: 101-107. Sturdee DW, Wilson RA, Pipili E, Cracker AD. Physiological aspects of menopausal hot flush. Br Med J 1978; 2: 79-80. Silverman RW, Bajorek JG, Lomax P, Tataryn IV. Monitoring the pathophysiological correlates of post-menopausal hot flushes. Maturitas 1981; 3: 39-46. Molnar GW. Investigation of hot flushes by ambulatory monitoring. Am J Physiol 1979; 237: 307-310.