To Pulse or Not to Pulse, Is That the Question?

Floras, John S.; Rao, Vivek; Billia, Filio

doi:10.1161/circulationaha.115.019461

Cited by 6 publications

(5 citation statements)

References 20 publications

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“…Moreover, even in the paediatric population, not all available pulsatile pumps generate this higher haemodynamic energy when compared with non-pulsatile pumps [31]. Mitigated pulsatility, however, which is frequently observed in ECMO patients early after implant, appears to be similar to non-pulsatile flow as it also increases muscular sympathetic nerve activity [32]. Furthermore, long duration of diastole and low levels of diastolic pressure elicited sympathetic bursts in CF LVAD as well as in VA-ECMO patients with minimal pulsatility [32].…”

Section: Discussionmentioning

confidence: 99%

“…Mitigated pulsatility, however, which is frequently observed in ECMO patients early after implant, appears to be similar to non-pulsatile flow as it also increases muscular sympathetic nerve activity [32]. Furthermore, long duration of diastole and low levels of diastolic pressure elicited sympathetic bursts in CF LVAD as well as in VA-ECMO patients with minimal pulsatility [32]. Interestingly in this context, 2 h after exposure to VA-ECMO with a high flow rate (120–150 mL/kg/min), decreased NO production was noted in cerebral arteries of lambs indicating impaired cerebral vascular endothelial function [33].…”

Section: Discussionmentioning

confidence: 99%

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Non-pulsatile blood flow is associated with enhanced cerebrovascular carbon dioxide reactivity and an attenuated relationship between cerebral blood flow and regional brain oxygenation

et al. 2019

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BackgroundSystemic blood flow in patients on extracorporeal assist devices is frequently not or only minimally pulsatile. Loss of pulsatile brain perfusion, however, has been implicated in neurological complications. Furthermore, the adverse effects of absent pulsatility on the cerebral microcirculation are modulated similarly as CO2 vasoreactivity in resistance vessels. During support with an extracorporeal assist device swings in arterial carbon dioxide partial pressures (PaCO2) that determine cerebral oxygen delivery are not uncommon—especially when CO2 is eliminated by the respirator as well as via the gas exchanger of an extracorporeal membrane oxygenation machine. We, therefore, investigated whether non-pulsatile flow affects cerebrovascular CO2 reactivity (CVR) and regional brain oxygenation (rSO2).MethodsIn this prospective, single-centre case-control trial, we studied 32 patients undergoing elective cardiac surgery. Blood flow velocity in the middle cerebral artery (MCAv) as well as rSO2 was determined during step changes of PaCO2 between 30, 40, and 50 mmHg. Measurements were conducted on cardiopulmonary bypass during non-pulsatile and postoperatively under pulsatile blood flow at comparable test conditions. Corresponding changes of CVR and concomitant rSO2 alterations were determined for each flow mode. Each patient served as her own control.ResultsMCAv was generally lower during hypocapnia than during normocapnia and hypercapnia (p < 0.0001). However, the MCAv/PaCO2 slope during non-pulsatile flow was 14.4 cm/s/mmHg [CI 11.8–16.9] and 10.4 cm/s/mmHg [CI 7.9–13.0] after return of pulsatility (p = 0.03). During hypocapnia, non-pulsatile CVR (4.3 ± 1.7%/mmHg) was higher than pulsatile CVR (3.1 ± 1.3%/mmHg, p = 0.01). Independent of the flow mode, we observed a decline in rSO2 during hypocapnia and a corresponding rise during hypercapnia (p < 0.0001). However, the relationship between ΔrSO2 and ΔMCAv was less pronounced during non-pulsatile flow.ConclusionsNon-pulsatile perfusion is associated with enhanced cerebrovascular CVR resulting in greater relative decreases of cerebral blood flow during hypocapnia. Heterogenic microvascular perfusion may account for the attenuated ΔrSO2/ΔMCAv slope. Potential hazards related to this altered regulation of cerebral perfusion still need to be assessed.Trial registrationThe study was retrospectively registered on October 30, 2018, with Clinical Trial.gov (NCT03732651).

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Non-pulsatile blood flow is associated with enhanced cerebrovascular carbon dioxide reactivity and an attenuated relationship between cerebral blood flow and regional brain oxygenation

et al. 2019

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“…[13][14][15][16][17] At rest, the principal stimulus to a burst occurrence is diminution of the restraint on central vasomotor neuron activity imposed by the arterial baroreceptor reflex. 16 With the probability of baroreceptor afferent nerve firing being greatest in systole, and least at end-diastole, 18,19 under basal conditions, when Mayer waves are most evident, muscle sympathetic firing frequency can be observed to rise and fall over ≈10 to12 s cycles, coherent with antecedent descents and ascents in diastolic BP. Bursts appear 1.1 to 1.3 s after the electrocardiographic R wave in relation to subject height and efferent conduction velocity.…”

Section: Msna and Vascular Resistancementioning

confidence: 99%

From Brain to Blood Vessel: Insights From Muscle Sympathetic Nerve Recordings

Floras

2021

Hypertension

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Multiunit recordings of postganglionic sympathetic outflow to muscle yield otherwise imperceptible insights into sympathetic neural modulation of human vascular resistance and blood pressure. This Corcoran Lecture will illustrate the utility of microneurography to investigate neurogenic cardiovascular regulation; review data concerning muscle sympathetic nerve activity of women and men with normal and high blood pressure; explore 2 concepts, central upregulation of muscle sympathetic outflow and cortical autonomic neuroplasticity; present sleep apnea as an imperfect model of neurogenic hypertension; and expose the paradox of sympathetic excitation without hypertension. In awake healthy normotensive individuals, resting muscle sympathetic nerve activity increases with age, sleep fragmentation, and obstructive apnea. Its magnitude is not signaled by heart rate. Age-related changes are nonlinear and differ by sex. In men, sympathetic nerve activity increases with age but without relation to their blood pressure, whereas in women, both rise concordantly after age 40. Mean values for muscle sympathetic nerve activity burst incidence are consistently higher in cohorts with hypertension than in matched normotensives, yet women’s sympathetic nerve traffic can increase 3-fold between ages 30 and 70 without causing hypertension. Thus, increased sympathetic nerve activity may be necessary but is insufficient for primary hypertension. Moreover, its inhibition does not consistently decrease blood pressure. Despite a half-century of microneurographic research, large gaps remain in our understanding of the content of the sympathetic broadcast from brain to blood vessel and its specific individual consequences for circulatory regulation and cardiovascular, renal, and metabolic risk.

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“…This unique physiological state can be detected in large and medium-sized arteries and varies between patients as shown in more detail in Figure 2 (Castagna et al, 2017). Accordingly, there has been much debate around the role of the arterial pulse (Cornwell, Tarumi, Lawley, & Ambardekar, 2019;Cornwell, Urey, Drazner, & Levine, 2015;Floras, Rao, & Billia, 2015;Stöhr, McDonnell, Colombo, & Willey, 2019). The fact that the overall health of LVAD patients continues to improve suggests that humans may not need a pulse to live.…”

Section: Who Are the 'Bionic Women And Men'?mentioning

confidence: 99%

Bionic women and men ‐ Part 1: Cardiovascular lessons from heart failure patients implanted with left ventricular assist devices

Stöhr

Cornwell

Kanwar

et al. 2020

Experimental Physiology

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Some humans with chronic, advanced heart failure are surgically implanted with a left ventricular assist device (LVAD). Because the LVAD produces a continuous flow, a palpable pulse is often absent in these patients. This allows for a unique investigation of the human circulation and has created a controversy around the 'need' for a pulse. The medical debate has also generated a more generic, fundamental discussion into what is 'normal' arterial physiology and health. The comprehensive study and understanding of the arterial responses to drastically altered haemodynamics due to continuous-flow LVADs, at rest and during activity, presents an opportunity to significantly increase our current understanding of the fundamental components of arterial regulation (flow, blood pressure, sympathetic activity, endothelial function, pulsatility) in a way that could never have been studied previously. In a series of four articles, we summarize the talks presented at the symposium entitled 'Bionic women and men-Physiology lessons from implantable cardiac devices' presented at the 2019 Annual Meeting of The Physiological Society in Aberdeen, UK. The articles highlight the novel questions generated by physiological phenomena observed in LVAD patients and propose future areas of interest within the field of cardiovascular physiology.

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To Pulse or Not to Pulse, Is That the Question?

Cited by 6 publications

References 20 publications

Non-pulsatile blood flow is associated with enhanced cerebrovascular carbon dioxide reactivity and an attenuated relationship between cerebral blood flow and regional brain oxygenation

Non-pulsatile blood flow is associated with enhanced cerebrovascular carbon dioxide reactivity and an attenuated relationship between cerebral blood flow and regional brain oxygenation

From Brain to Blood Vessel: Insights From Muscle Sympathetic Nerve Recordings

Bionic women and men ‐ Part 1: Cardiovascular lessons from heart failure patients implanted with left ventricular assist devices

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