Ventilatory baroreflex sensitivity in humans is not modulated by chemoreflex activation

Abstract

IL, Ocon AJ, Taneja I, Terilli C, Medow MS. Ventilatory baroreflex sensitivity in humans is not modulated by chemoreflex activation. Am J Physiol Heart Circ Physiol 300: H1492-H1500, 2011. First published February 11, 2011 doi:10.1152/ajpheart.01217.2010.-Increasing arterial blood pressure (AP) decreases ventilation, whereas decreasing AP increases ventilation in experimental animals. To determine whether a "ventilatory baroreflex" exists in humans, we studied 12 healthy subjects aged 18 -26 yr. Subjects underwent baroreflex unloading and reloading using intravenous bolus sodium nitroprusside (SNP) followed by phenylephrine ("Oxford maneuver") during the following "gas conditions:" room air, hypoxia (10% oxygen)-eucapnia, and 30% oxygen-hypercapnia to 55-60 Torr. Mean AP (MAP), heart rate (HR), cardiac output (CO), total peripheral resistance (TPR), expiratory minute ventilation (V E), respiratory rate (RR), and tidal volume were measured. After achieving a stable baseline for gas conditions, we performed the Oxford maneuver. V E increased from 8.8 Ϯ 1.3 l/min in room air to 14.6 Ϯ 0.8 l/min during hypoxia and to 20.1 Ϯ 2.4 l/min during hypercapnia, primarily by increasing tidal volume. V E doubled during SNP. CO increased from 4.9 Ϯ .3 l/min in room air to 6.1 Ϯ .6 l/min during hypoxia and 6.4 Ϯ .4 l/min during hypercapnia with decreased TPR. HR increased for hypoxia and hypercapnia. Sigmoidal ventilatory baroreflex curves of V E versus MAP were prepared for each subject and each gas condition. Averaged curves for a given gas condition were obtained by averaging fits over all subjects. There were no significant differences in the average fitted slopes for different gas conditions, although the operating point varied with gas conditions. We conclude that rapid baroreflex unloading during the Oxford maneuver is a potent ventilatory stimulus in healthy volunteers. Tidal volume is primarily increased. Ventilatory baroreflex sensitivity is unaffected by chemoreflex activation, although the operating point is shifted with hypoxia and hypercapnia.baroreceptors; ventilation; blood pressure In intact animals (dogs) hyperpnea follows occlusion of the common carotid arteries; it is wholly reflex in origin because the effect is the same even though all branches of the carotids have been previously tied excepting only the lingual arteries, and because section of the sinus nerves completely abolishes the reaction.Carl F. Schmidt (45) DETECTION OF ARTERIAL BLOOD PRESSURE (AP) by the arterial baroreceptors causes changes in heart rate (HR), sympathetic vasoconstriction, adrenal function, and renal sympathetic activity (2, 5). Evidence primarily derived from animal experiments suggests that the carotid sinus baroreflex also affects respiratory function (7,26,45,48). Rapidly increasing blood pressure causes decreased ventilation, whereas decreasing blood pressure causes increased ventilation. While these ventilatory effects were at one time attributed to increased or decreased perfusion of the arterial chemoreceptors (26, 32), s...

Baroreflex regulation affects ventilation in the Cururu toad Rhinella schneideri

“…Pharmacologically induced changes in blood pressure not only triggered baroreflex responses in f H but also affected _ V E in R. schneideri, similar to what has been reported for mammals (Brunner et al, 1982;Walker and Jennings, 1998;McMullan and Pilowsky, 2010;Stewart et al, 2011). Increases in blood pressure in the toads were followed by reductions in _ V E , primarily through modification of f R and to a lesser extent V T ; conversely, _ V E was significantly increased during hypotension.…”

“…Generated extravascular fluid in anuran amphibians returns to the cardiovascular system through a combination of changes in pressure and volume of the lymph sacs that is driven by effectors such as lung ventilation (inflation and deflation) and skeletal muscle contraction Hedrick et al, 2007). Therefore, from an evolutionary perspective, ventilatory responses that may be modulated by baroreceptor loading and unloading in R. schneideri can contribute to our understanding of a number of pieces of evidence for the influence of the cardiovascular system on the respiratory system in mammals (Brunner et al, 1982;Walker and Jennings, 1998;Baekey et al, 2010;McMullan and Pilowsky, 2010;Stewart et al, 2011). More interestingly, our findings add further support to a role for lung ventilation in blood pressure/volume homeostasis in anuran amphibians , although the relationship between pulmonary ventilation, baroreflex and lymphatic system in our toads is still correlational rather than mechanistic.…”

Cerebral oxygenation following epinephrine infusion

“…Alternatively, β-adrenergic stimulation increases resting ventilation and reflex chemosensitivity [22,23], and baroreflex activity is inversely related to ventilation (i.e. a drop in pressure, as observed in the present study, may elicit an increase in ventilation) [24]. Such an increase in ventilation could reduce arterial PCO 2 and affect global CBF.…”

C1 neurons: the body's EMTs

“…Using optogenetics, we have shown that selective C1 neuron stimulation activates breathing in conscious mice (1). Barosensitive C1 neurons presumably contribute to the ventilatory baroreflex; i.e., the breathing stimulation elicited by hypotension, well described in conscious humans (173).…”