Effects of body position on the ventilatory response to hypercapnia

Donina, Zh. A.; Ga, Danilova; Aleksandrova, N. P.

doi:10.1186/2047-783x-14-s4-63

Cited by 2 publications

(1 citation statement)

References 13 publications

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“…Notably, we observed hypoxic ventilatory decline during 10 min of continued hypoxia, as well as ventilatory acclimatization to hypoxia with increases in the isocapnic HVR after 2 days of sustained hypoxia (38). The resting ventilation in our study is smaller than in other literature studies, since the subjects were lying supine within the MRI scanner (13,43) (whereas other studies have subjects upright or semirecumbent). Unlike ventilation, CBF shows a constant sensitivity (slope) to desaturation across a wide range of Sa O 2 , and there is no cerebrovascular equivalent of hypoxic ventilatory decline in the cerebral circulation.…”

Section: Discussioncontrasting

confidence: 55%

Evidence from high-altitude acclimatization for an integrated cerebrovascular and ventilatory hypercapnic response but different responses to hypoxia

Smith

Krizay

Sá

et al. 2017

Journal of Applied Physiology

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Ventilation and cerebral blood flow (CBF) are both sensitive to hypoxia and hypercapnia. To compare chemosensitivity in these two systems, we made simultaneous measurements of ventilatory and cerebrovascular responses to hypoxia and hypercapnia in 35 normal human subjects before and after acclimatization to hypoxia. Ventilation and CBF were measured during stepwise changes in isocapnic hypoxia and iso-oxic hypercapnia. We used MRI to quantify actual cerebral perfusion. Measurements were repeated after 2 days of acclimatization to hypoxia at 3,800 m altitude (partial pressure of inspired O = 90 Torr) to compare plasticity in the chemosensitivity of these two systems. Potential effects of hypoxic and hypercapnic responses on acute mountain sickness (AMS) were assessed also. The pattern of CBF and ventilatory responses to hypercapnia were almost identical. CO responses were augmented to a similar degree in both systems by concomitant acute hypoxia or acclimatization to sustained hypoxia. Conversely, the pattern of CBF and ventilatory responses to hypoxia were markedly different. Ventilation showed the well-known increase with acute hypoxia and a progressive decline in absolute value over 25 min of sustained hypoxia. With acclimatization to hypoxia for 2 days, the absolute values of ventilation and O sensitivity increased. By contrast, O sensitivity of CBF or its absolute value did not change during sustained hypoxia for up to 2 days. The results suggest a common or integrated control mechanism for CBF and ventilation by CO but different mechanisms of O sensitivity and plasticity between the systems. Ventilatory and cerebrovascular responses were the same for all subjects irrespective of AMS symptoms. NEW & NOTEWORTHY Ventilatory and cerebrovascular hypercapnic response patterns show similar plasticity in CO sensitivity following hypoxic acclimatization, suggesting an integrated control mechanism. Conversely, ventilatory and cerebrovascular hypoxic responses differ. Ventilation initially increases but adapts with prolonged hypoxia (hypoxic ventilatory decline), and ventilatory sensitivity increases following acclimatization. In contrast, cerebral blood flow hypoxic sensitivity remains constant over a range of hypoxic stimuli, with no cerebrovascular acclimatization to sustained hypoxia, suggesting different mechanisms for O sensitivity in the two systems.

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Section: Discussioncontrasting

confidence: 55%

Evidence from high-altitude acclimatization for an integrated cerebrovascular and ventilatory hypercapnic response but different responses to hypoxia

Smith

Krizay

Sá

et al. 2017

Journal of Applied Physiology

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A rapid rotation to an inverted seated posture inhibits muscle force, activation, heart rate and blood pressure

Johar

Grover

DiSanto³

et al. 2013

Eur J Appl Physiol

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Although previous studies have demonstrated neuromuscular and cardiovascular changes with slow inversion rates, emergencies, such as overturned vehicles and helicopters can occur rapidly. The purpose of this study was to investigate changes in neuromuscular and cardiovascular responses with rapid (1 s) and slower (3 s) transitions from upright to inverted seated positions. Twenty-two subjects performed separate and concurrent unilateral elbow flexion and leg extension maximal voluntary contractions (MVCs) for 6 s in an upright seated position and when inverted with 1 and 3 s rotations. Elbow flexion and leg extension force; biceps, triceps, quadriceps and hamstrings electromyographic (EMG) activity, heart rate (HR), systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured. Whether the elbow flexion or leg extension contractions occurred concurrently or individually, significant (p < 0.05) decreases in MVC force and EMG activity were found when inverted within 1 and 3 s rotations as compared to upright. Triceps and hamstrings EMG activity (p < 0.05) decreased when inverted within 1 s rotation as compared to upright. Following rotation, the maintenance of the inverted position (3-6 s timepoint) resulted in a significant (p < 0.05) increase in leg extension MVC as compared to the initial second of rotation to inversion. HR, SBP and DBP demonstrated (p < 0.001) decreases when inverted within 1 and 3 s rotations as compared to upright. In conclusion, this is the first study to show that irrespective of rotation speed, inversion inhibited neuromuscular and cardiovascular responses, similar to the more deliberate, slower rotation of previous inversion studies.

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Effects of body position on the ventilatory response to hypercapnia

Cited by 2 publications

References 13 publications

Evidence from high-altitude acclimatization for an integrated cerebrovascular and ventilatory hypercapnic response but different responses to hypoxia

Evidence from high-altitude acclimatization for an integrated cerebrovascular and ventilatory hypercapnic response but different responses to hypoxia

A rapid rotation to an inverted seated posture inhibits muscle force, activation, heart rate and blood pressure

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