Effects of acid-base imbalance on vascular reactivity

Abstract

Acid-base homeostasis maintains systemic arterial pH within a narrow range. Whereas the normal range of pH for clinical laboratories is 7.35-7.45, in vivo pH is maintained within a much narrower range. In clinical and experimental settings, blood pH can vary in response to respiratory or renal impairment. This altered pH promotes changes in vascular smooth muscle tone with impact on circulation and blood pressure control. Changes in pH can be divided into those occurring in the extracellular space (pH o ) and those occurring within the intracellular space (pH i ), although, extracellular and intracellular compartments influence each other. Consistent with the multiple events involved in the changes in tone produced by altered pH o , including type of vascular bed, several factors and mechanisms, in addition to hydrogen ion concentration, have been suggested to be involved. The scientific literature has many reports concerning acid-base balance and endothelium function, but these concepts are not clear about acid-base disorders and their relations with the three known mechanisms of endothelium-dependent vascular reactivity: nitric oxide (NO/cGMP-dependent), prostacyclin (PGI 2 /cAMP-dependent) and hyperpolarization. During the last decades, many studies have been published and have given rise to confronting data on acid-base disorder and endothelial function. Therefore, the main proposal of this review is to provide a critical analysis of the state of art and incentivate researchers to develop more studies about these issues.

Rapid magnetic resonance measurement of global cerebral metabolic rate of oxygen consumption in humans during rest and hypercapnia

“…The initial changes in pH are likely offset, at least in part, by local tissue buffering at the intracellular and extracellular level (Celotto et al, 2008). However, as the hypercapnic stimulus persists and the steady-state parenchymal pCO 2 value is reached, these local homoeostatic measures are overwhelmed.…”

An attempt to use the peritoneal cavity fluid in the diagnostics of acid-base balance disorders in dogs

“…Intracellular pH regulation is mainly based on equilibrium between molecular mechanisms which cause constant inflow to and removal of H + from the cell. Removal of H + takes place through exchange with Na + and requires some energy, whereas inflow of H + is a passive process and is involved in an exchange with Cl - (Boron 2004, Balakrishnan et al 2007, Celotto et al 2008. Our own research showed that concentration of ions serving for calculation of SID and Atot in the peritoneal cavity fluid is very variable.…”

Presentation of an experimental method to induce in vitro ("organ chambers") respiratory acidosis and its effect on vascular reactivity

“…The mechanisms by which pH influences vascular tone or their response to specific agonists are not yet fully understood, but there is some evidence to suggest the involvement of nitric oxide (NO), prostacyclin (PGI 2 ), channels for potassium and calcium flux 3 .…”

“…The literature presents well-designed methods to produce metabolic acidosis in vitro [3][4][5] . However, methods to induce respiratory acidosis are rare.…”

“…Acid-base shifts are caused by pCO 2 changes (respiratory mechanisms) and addition of acid or base (non-respiratory mechanisms).These shifts affect the vascular reactivity, and, besides the direct effect on vascular tone, may also alter vascular vasoconstrictor and/or vasodilatorsresponsiveness [1][2][3] .…”