Time domains of the hypoxic ventilatory response in ectothermic vertebrates

Over a decade has passed since Powell et al. (Respir Physiol 112:123–134, 1998) described and defined the time domains of the hypoxic ventilatory response (HVR) in adult mammals. These time domains, however, have yet to receive much attention in other vertebrate groups. The initial, acute HVR of fish, amphibians and reptiles serves to minimize the imbalance between oxygen supply and demand. If the hypoxia is sustained, a suite of secondary adjustments occur giving rise to a more long-term balance (acclimatization) that allows the behaviors of normal life. These secondary responses can change over time as a function of the nature of the stimulus (the pattern and intensity of the hypoxic exposure). To add to the complexity of this process, hypoxia can also lead to metabolic suppression (the hypoxic metabolic response) and the magnitude of this is also time dependent. Unlike the original review of Powell et al. (Respir Physiol 112:123–134, 1998) that only considered the HVR in adult animals, we also consider relevant developmental time points where information is available. Finally, in amphibians and reptiles with incompletely divided hearts the magnitude of the ventilatory response will be modulated by hypoxia-induced changes in intra-cardiac shunting that also improve the match between O2 supply and demand, and these too change in a time-dependent fashion. While the current literature on this topic is reviewed here, it is noted that this area has received little attention. We attempt to redefine time domains in a more ‘holistic’ fashion that better accommodates research on ectotherms. If we are to distinguish between the genetic, developmental and environmental influences underlying the various ventilatory responses to hypoxia, however, we must design future experiments with time domains in mind

Autonomic function in hypertensive and normotensive subjects - The importance of gender

Baroreceptor reflex sensitivity (BRS) has been found lower and heart rate variability (HRV) parasympathetic markers have been found higher in healthy women than in healthy men. Thus, in the present study we hypothesized gender differences in the autonomic function among hypertensive subjects. Forty-one hypertensive patients and 34 normotensive subjects, age 53 +/-1 years, were examined. Four weeks after cessation of antihypertensive therapy, HRV was assessed in 24-hour Holter ECGs, and BRS was calculated with the transfer technique. A t test was performed after log transformation of spectral values. Resting blood pressure and heart rate in the hypertensive and the normotensive groups were 150 +/-2/100 +/-1 (mean +/- SEM) and 121 +/-2/81 +/-1 mmHg, respectively, and 68 +/-1 and 60 +/-1 bpm, respectively (