Effects of human pregnancy on the ventilatory chemoreflex response to carbon dioxide

Abstract

This study examined the effects of human pregnancy on the central chemoreflex control of breathing. Subjects were two groups ( n = 11) of pregnant subjects (PG, gestational age, 36.5 ± 0.4 wk) and nonpregnant control subjects (CG), equated for mean age, body height, prepregnant body mass, parity, and aerobic fitness. All subjects performed a hyperoxic CO2 rebreathing procedure, which includes prior hyperventilation and maintenance of iso-oxia. Resting blood gases and plasma progesterone and estradiol concentrations were measured. During rebreathing trials, end-tidal Pco2 increased, whereas end-tidal Po2 was maintained at a constant hyperoxic level. The point at which ventilation (V̇e) began to rise as end-tidal Pco2 increased was identified as the central chemoreflex ventilatory recruitment threshold for CO2 (VRTco2). V̇e levels below (basal V̇e) and above (central chemoreflex sensitivity) the VRTco2 were determined. The VRTco2 was significantly lower in the PG vs. CG (40.5 ± 0.8 vs. 45.8 ± 1.6 Torr), and both basal V̇e (14.8 ± 1.1 vs. 9.3 ± 1.6 l/min) and central chemoreflex sensitivity (5.07 ± 0.74 vs. 3.16 ± 0.29 l·min−1·Torr−1) were significantly higher in the PG vs. CG. Pooled data from the two groups showed significant correlations for resting arterial Pco2 with basal V̇e, central chemoreflex sensitivity, and the VRTco2. The VRTco2 was also correlated with progesterone and estradiol concentrations. These data support the hypothesis that pregnancy decreases the threshold and increases the sensitivity of the central chemoreflex response to CO2. These changes may be due to the effects of gestational hormones on chemoreflex and/or nonchemoreflex drives to breathe.

Gestation increases the energetic cost of breathing in the lizard, Tiliqua rugosa

“…In this study and in studies in humans, increases in the rate of inspiration during pregnancy reflect an increased respiratory drive (Kolarzyk et al, 2005). In humans, at least, this increase in the rate of inspiration during pregnancy may be associated with overcoming increased respiratory system resistance (Kolarzyk et al, 2005) and/or may be linked with progesterone-associated changes in central chemosensitivity (Jensen et al, 2005). It is likely that lung compression during pregnancy in T. rugosa decreases lung compliance and an increase in the rate of inspiration may be an advantageous compensatory response.…”

Effect of menopause on the chemical control of breathing and its relationship with acid-base status

“…Withdrawal of these hormones would therefore be expected to decrease resting V E, thereby increasing Pa CO 2 in otherwise healthy postmenopausal women. Although the underlying mechanisms of these ventilatory adaptations remain speculative, the combined facilitatory effects of P 4 and E 2 on central and/or peripheral chemoreflex drives to breathe may be involved (3,4,11,26,28,29,31,48 (18 -21), this is the first study to examine the role of acid-base balance in the chemoreflex control of breathing in healthy postmenopausal women.In the present study, we postulated that reductions in circulating female sex hormone concentrations, alone or in combination with the alkalizing effect of an increased plasma [SID], contribute significantly to the relative hypoventilation and attendant arterial hypercapnia observed after the onset of menopause. We hypothesized that these outcomes would be mechanistically linked to reductions in central and peripheral chemoreflex drives to breathe.…”

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(25,28,40,48,51,54). Hormone replacement therapy studies reported that medroxyprogesterone acetate (a synthetic progestin), administered alone and in combination with E 2 , consistently reduced resting Pa CO 2 by ϳ6 mmHg in postmenopausal women (39,(43)(44)(45)(46).

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Progesterone in Human Pregnancy and Parturition

“…As a consequence, maternal arterial pH is increased to 7.46. The increased respiratory effort and decrease in PCO 2 has been related to progesterone and to a lesser degree to estrogen (Wolfe et al 1998, Jensen et al 2005.…”