Inspiratory resistance delays the reporting of symptoms with central hypovolemia: association with cerebral blood flow

Rickards, Caroline A.; Ryan, Kathy L.; Cooke, William H.; Lurie, Keith G.; Convertino, Víctor A.

doi:10.1152/ajpregu.00087.2007

Cited by 56 publications

(66 citation statements)

References 36 publications

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“…Although increased mean cerebral blood velocity was observed in human subjects breathing through an ITD set at 7 cm H 2 O pressure difference in a human model of central hypovolemia, 12 breathing through a low level of resistance unexpectedly failed to ameliorate the reduction in mean cerebral blood velocity. 7,27 A novel finding, however, was a significant increase in the amplitude of cerebral blood velocity oscillations associated with inspiratory impedance breathing during reduced central blood volume. 7,27 A recent preliminary examination of individual oscillatory waveforms also revealed a significant increase in the duration of each oscillation, so that oscillations occurred at a lower frequency during ITD breathing (Fig.…”

Section: Patient Tolerance and Response To Acute Central Hypovolemia mentioning

confidence: 98%

“…7,27 A novel finding, however, was a significant increase in the amplitude of cerebral blood velocity oscillations associated with inspiratory impedance breathing during reduced central blood volume. 7,27 A recent preliminary examination of individual oscillatory waveforms also revealed a significant increase in the duration of each oscillation, so that oscillations occurred at a lower frequency during ITD breathing (Fig. 8).…”

Section: Patient Tolerance and Response To Acute Central Hypovolemia mentioning

confidence: 98%

“…The delay in the onset of symptoms with the active ITD breathing might suggest that more sustained maximum velocities induced by enhanced negative intrathoracic pressure are a protective mechanism for maintaining adequate perfusion, which prolongs central nervous system tolerance to reduced central blood volume, even in the presence of hypotension. 7,27 In addition to its effects on cerebral blood velocity dynamics, animal studies found that decreased intrathoracic pressure causes an immediate, proportionate reduction in intracranial pressure (Fig. 9).…”

Section: Patient Tolerance and Response To Acute Central Hypovolemia mentioning

confidence: 99%

“…We propose that the impact of this physiology underlies, in part, the delay in onset of symptoms in subjects using the ITD while undergoing progressive reduction in central blood volume that mimics hemorrhage. 7 The multi-factorial effects of inspiration through a low level of resistance to harness the thoracic pump, and its consequent effect on cerebral perfusion, systemic circulation, and increased coherence between arterial blood pressure and sympathetic nerve activity improved survival rate in animals after severe hemorrhage. 26 Although studies focused on survival in humans under similar conditions have not yet been performed, investigations in patients 11 and research subjects 17,13,24 have shown a hemodynamic benefit in the setting of clinically symptomatic hypotension, as described below.…”

Section: Patient Tolerance and Response To Acute Central Hypovolemia mentioning

confidence: 99%

“…Studies have shed light on how to easily use the thoracic pump to augment venous blood flow return, lower intracranial pressure, and regulate cardiopulmonary-cerebral blood flow in spontaneously breathing individuals and in patients in cardiac arrest receiving cardiopulmonary resuscitation (CPR). [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] Mechanisms Underlying the Hemodynamic Effectiveness of the Respiratory Pump…”

Section: Introductionmentioning

confidence: 99%

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Optimizing the Respiratory Pump: Harnessing Inspiratory Resistance to Treat Systemic Hypotension

et al. 2011

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We review the physiology and affects of inspiration through a low level of added resistance for the treatment of hypotension. Recent animal and clinical studies demonstrated that one of the body's natural response mechanisms to hypotension is to harness the respiratory pump to increase circulation. That finding is consistent with observations, in the 1960s, about the effect of lowering intrathoracic pressure on key physiological and hemodynamic variables. We describe studies that focused on the fundamental relationship between the generation of negative intrathoracic pressure during inspiration through a low level of resistance created by an impedance threshold device and the physiologic sequelae of a respiratory pump. A decrease in intrathoracic pressure during inspiration through a fixed resistance resulting in a pressure difference of 7 cm H 2 O has multiple physiological benefits, including: enhanced venous return and cardiac stroke volume, lower intracranial pressure, resetting of the cardiac baroreflex, elevated cerebral blood flow oscillations, increased tissue blood flow/pressure gradient, and maintenance of the integrity of the baroreflexmediated coherence between arterial pressure and sympathetic nerve activity. While breathing has traditionally been thought primarily to provide gas exchange, studies of the mechanisms involved in animals and humans provide the physiological underpinnings for "the other side of breathing": to increase circulation to the heart and brain, especially in the setting of physiological stress. The existing results support the use of the intrathoracic pump to treat clinical conditions associated with hypotension, including orthostatic hypotension, hypotension during and after hemodialysis, hemorrhagic shock, heat stroke, septic shock, and cardiac arrest. Harnessing these fundamental mechanisms that control cardiopulmonary physiology provides new opportunities for respiratory therapists and others who have traditionally focused on ventilation to also help treat serious and often life-threatening circulatory disorders.

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Section: Patient Tolerance and Response To Acute Central Hypovolemia mentioning

confidence: 98%

Section: Patient Tolerance and Response To Acute Central Hypovolemia mentioning

confidence: 98%

Section: Patient Tolerance and Response To Acute Central Hypovolemia mentioning

confidence: 99%

Section: Patient Tolerance and Response To Acute Central Hypovolemia mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Optimizing the Respiratory Pump: Harnessing Inspiratory Resistance to Treat Systemic Hypotension

et al. 2011

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Cerebrovascular Neuroprotection after Acute Concussion in Adolescents

Aaron

Hamner

Ozturk

et al. 2021

Annals of Neurology

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Objective: To assess acute cerebrovascular function in concussed adolescents (14-21 years of age), whether it is related to resting cerebral hemodynamics, and whether it recovers chronically. Methods: Cerebral vasoreactivity and autoregulation, based on middle cerebral artery blood flow velocity, was assessed in 28 concussed participants (≤14 days of injury) and 29 matched controls. The participants in the concussion group returned for an 8-week follow-up assessment. Over the course of those 8-weeks, participants recorded aerobic exercise frequency and duration. Results: Between groups, demographic, clinical, and hemodynamic variables were not significantly different. Vasoreactivity was significantly higher in the concussed group (p = 0.02). Within the concussed group, 60% of the variability in resting cerebral blood flow velocity was explained by vasoreactivity and two components of autoregulationfalling slope and effectiveness of autoregulation (adjusted R 2 = 0.60, p < 0.001). Moreover, lower mean arterial pressure, lower responses to increases in arterial pressure, and lower vasoreactivity were significantly associated with larger symptom burden (adjusted R 2 = 0.72, p < 0.01). By the 8-week timepoint, symptom burden, but not vasoreactivity, improved in all but four concussed participants (p < 0.01). 8-week change in vasoreactivity was positively associated with aerobic exercise volume (adjusted R 2 = 0.19, p = 0.02). Interpretation: Concussion resulted in changes in cerebrovascular regulatory mechanisms, which in turn explained the variability in resting cerebral blood flow velocity and acute symptom burden. Furthermore, these alterations persisted chronically despite symptom resolution, but was positively modified by aerobic exercise volume. These findings provide a mechanistic framework for further investigation into underlying cerebrovascular related symptomatology.

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Cerebral Blood‐Flow Regulation During Hemorrhage

Rickards

2015

Comprehensive Physiology

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Massive uncontrolled blood loss can occur under a variety of conditions including trauma, as a complication of childbirth or surgery, ruptured ulcers, clotting disorders, and hemorrhagic fevers. Across the continuum of hemorrhage, loss of blood volume is a significant challenge to the maintenance of cerebral perfusion. During the initial stages of hemorrhage, reflex mechanisms are activated to protect cerebral perfusion, but persistent blood loss will eventually reduce global cerebral blood flow and the delivery of metabolic substrates, leading to generalized cerebral ischemia, hypoxia, and ultimately, neuronal cell death. Cerebral blood flow is controlled by various regulatory mechanisms, including prevailing arterial pressure, intracranial pressure, arterial blood gases, neural activity, and metabolic demand. Hemorrhage represents a unique physiological stress to the brain, as it influences each of these regulatory mechanisms, resulting in complex interplay that ultimately challenges the ability of the brain to maintain adequate perfusion. Early studies of actual hemorrhage in humans employed blood loss protocols up to 1000 mL, but did not include any measurements of cerebral blood flow. As ethical considerations necessarily constrain the use of human volunteers for massive blood loss studies that induce irreversible shock, most of what is known about cerebral blood-flow responses to hemorrhage has been determined from animal models. Limitations of species differences regarding regulatory mechanisms, anatomy, and the effect of anesthesia, however, must be considered. Advances in monitoring technologies, and a recent renewed interest in understanding cerebral blood-flow regulation in humans, however, is rapidly accelerating knowledge in this field.

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Inspiratory resistance delays the reporting of symptoms with central hypovolemia: association with cerebral blood flow

Cited by 56 publications

References 36 publications

Optimizing the Respiratory Pump: Harnessing Inspiratory Resistance to Treat Systemic Hypotension

Optimizing the Respiratory Pump: Harnessing Inspiratory Resistance to Treat Systemic Hypotension

Cerebrovascular Neuroprotection after Acute Concussion in Adolescents

Cerebral Blood‐Flow Regulation During Hemorrhage

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