Biomedical subjects

A P Heenan

Publications and source records attributed to A P Heenan.

5 recordsLinked to original sources

PubMed2003

Plasma osmolality and the strong ion difference predict respiratory adaptations in pregnant and nonpregnant women.

This study tested the hypothesis that plasma osmolality and the strong ion difference ([SID]) predict PaCO2 during rest and during exercise in physically active pregnant (n = 22; gestational age 37.0 +/- 0.2 weeks) and nonpregnant (n = 17) women. Nonpregnant subjects were in varying stages of the menstrual cycle. Arterialized blood gases, hydrogen ion concentration, plasma osmolality, [SID], and circulating levels of progesterone were measured at rest and during upright cycling at work rates corresponding to 70 and 110% of the ventilatory threshold. Pooled data from the two groups at rest revealed significant correlations (P < 0.05) between PaCO2 with plasma osmolality, [SID], and progesterone. Progesterone was also significantly correlated with [SID] and osmolality. Also, changes in PaCO2 with exercise correlated significantly with changes in [SID]. The results support the hypothesis that plasma osmolality and [SID] are important factors in the modulation of respiratory sensitivity in healthy women. Also, the effects of progesterone on PaCO2 may be expressed, at least in part, through progesterone-induced changes in [SID] and osmolality.

Adult↗

PubMed2001

Maximal exercise testing in late gestation: maternal responses.

OBJECTIVE: To study the effects of human pregnancy on metabolic and respiratory responses to maximal cycle ergometer testing and to test the hypothesis that the respiratory exchange ratio at maximal exercise and peak postexercise lactate concentration are lower in the pregnant compared with the nonpregnant state and that these effects are associated with lower excess postexercise oxygen consumption during pregnancy. METHODS: The pregnant (n = 14, mean gestational age 34.7 +/- 0.4 weeks) and nonpregnant control group (n = 14) included healthy, physically active women. Groups were matched for age, height, parity, prepregnant body mass and body mass index (BMI), and aerobic fitness. Breath-by-breath gas exchange was measured at rest, during exercise, and 15 minutes after exercise. The minimum sample size to detect a statistically significant result for a reasonable difference (0.25 L/min) in the ventilatory threshold was calculated to be ten subjects per group; thus, 14 was considered adequate. RESULTS: Maximal oxygen uptake, the ventilatory threshold, the point of respiratory compensation, and calculated work efficiency did not differ significantly between groups. However, the respiratory exchange ratio at maximal exercise, peak postexercise lactate, and excess postexercise oxygen consumption were significantly lower in the pregnant group. Peak lactate was significantly correlated with the respiratory exchange ratio and excess postexercise oxygen consumption. CONCLUSION: The capacity for weight-supported work is preserved in late gestation, and work efficiency is unchanged. However, carbohydrate utilization might be blunted at high levels of exertion. Blunted respiratory responses were attributed to reduced lactate production and/or dilution of lactate in an expanded blood volume.

Adult↗

PubMed2001

Physicochemical analysis of phasic menstrual cycle effects on acid-base balance.

In accordance with Stewart's physicochemical approach, the three independent determinants of plasma hydrogen ion concentration ([H(+)]) were measured at rest and during exercise in the follicular (FP) and luteal phase (LP) of the human menstrual cycle. Healthy, physically active women with similar physical characteristics were tested during either the FP (n = 14) or LP (n = 14). Arterialized blood samples were obtained at rest and after 5 min of upright cycling at both 70 and 110% of the ventilatory threshold (T(Vent)). Measurements included plasma [H(+)], arterial carbon dioxide tension (Pa(CO(2))), total weak acid ([A(Tot)]) as reflected by total protein, and the strong-ion difference ([SID]). The transition from rest to exercise in both groups resulted in a significant increase in [H(+)] at 70% T(Vent) versus rest and at 110% T(Vent) versus both rest and 70% T(Vent). No significant between-group differences were observed for [H(+)] at rest or in response to exercise. At rest in the LP, [A(Tot)] and Pa(CO(2)) were significantly lower (acts to decrease [H(+)]) compared with the FP. This effect was offset by a reduction in [SID] (acts to increase [H(+)]). After the transition from rest to exercise, significantly lower [A(Tot)] during the LP was again observed. Although the [SID] and Pa(CO(2)) were not significantly different between groups, trends for changes in these two variables were similar to changes in the resting state. In conclusion, mechanisms regulating [H(+)] exhibit phase-related differences to ensure [H(+)] is relatively constant regardless of progesterone-mediated ventilatory changes during the LP.

Acid-Base Equilibrium↗

PubMed2000

Plasma acid-base regulation above and below ventilatory threshold in late gestation.

Stewart's physicochemical approach was used to study the effects of pregnancy on acid-base regulation in arterialized blood. Responses of 15 healthy pregnant women (PG; gestational age, 37.1 +/- 0.2 wk) were compared with those of 15 nonpregnant controls (CG) at rest and during cycling at 70 and 110% of the ventilatory threshold (T(vent)). Hydrogen ion concentration ([H(+)]) was lower in the PG vs. CG at rest and during exercise (P < 0.05 at rest and 70% T(vent)). Exercise-induced changes in [H(+)] were similar between groups. Lower resting [H(+)] values in the PG vs. CG resulted from lower values for arterialized PCO(2) (Pa(CO(2))) and total weak acid ([A](tot)), which were partly offset by a lower strong-ion difference ([SID]). Reductions in [A](tot) and [SID] at rest were primarily the result of reductions in albumin [Alb] and sodium [Na(+)], respectively. In the transition from rest to 70% T(vent), small increases in Pa(CO(2)) and [A](tot) contributed to moderate increases in [H(+)] in both groups, however [SID] increased in the PG and decreased in the CG (P < 0.05 between groups). In the transition from rest to 110% T(vent), decreases in [SID] made a significantly greater contribution to changes in [H(+)] in the CG vs. PG. Exercise-induced increases in [H(+)] are similar in the pregnant vs. nonpregnant state, but there is a reduced contribution of [SID] both above and below T(vent) during pregnancy.

Acid-Base Equilibrium↗

PubMed1998

Acid-base regulation and control of ventilation in human pregnancy.

The purposes of this review were twofold: to apply modern physicochemical principles to explain changes in acid-base regulation and the control of ventilation in human pregnancy; and to demonstrate the value of pregnancy as a model for the study of endocrine effects on physiological control systems. Application of P.A. Stewart's approach (P.A. Stewart. Can. J. Physiol. Pharmacol. 61: 1444-1461, 1983) shows that lower values of plasma hydrogen ion concentration ([H+]) observed at rest and in association with exercise in pregnancy are the result of lower values for carbon dioxide tension (Pco2) and total weak acid ([A(tot)]). This effect is partly offset by a lower strong ion difference ([SID]). The ability to predict plasma [H+] at rest and following strenuous exercise in pregnancy (J.G. Kemp, F.A. Greer, and L.A. Wolfe. J. Appl. Physiol. 83: 644-651, 1997) supports the validity of Stewart's approach. Jennings and associates (D.B. Jennings. Can. J. Physiol. Pharmacol. 72: 1499-1512, 1994) have further demonstrated in animal models the involvement of plasma osmolality and circulating levels of angiotensin II (ANG II) and arginine vasopressin (AVP) in the chemical control of ventilation. We hypothesize that pregnancy-induced increases in respiratory sensitivity to carbon dioxide are the combined result of reduced plasma osmolality, reduced cerebrospinal fluid [SID], and augmented circulating levels of progesterone, ANG II, and AVP.

Acid-Base Equilibrium↗