Cerebrovascular and systemic hemodynamic response to carbon dioxide in humans.

BACKGROUND

Arterial partial pressure alteration of CO2 ((Equation is included in full-text article.)) affects not only the cerebral blood flow velocity but also the systemic arterial blood pressure (BP). At the same time, BP can affect the cerebral blood flow. The objective of the present research is to study the impact of the (Equation is included in full-text article.)level on cerebrovascular CO2 reactivity ((Equation is included in full-text article.)) and BP as well as the impact of BP upon (Equation is included in full-text article.)alteration by hypercapnia and hypocapnia.

MATERIALS AND

METHODS

Cerebral blood flow velocity was recorded by means of transcranial Doppler in both middle cerebral arteries (MCAv left and right). The mean arterial pressure (MAP) was studied using the finger photoplethysmography method, arterial blood oxygen saturation was estimated by the pulse oximetry method, and end-tidal (Equation is included in full-text article.)((Equation is included in full-text article.)) was measured with an infrared capnograph. After a recording of the reference values of all the parameters, all the volunteers underwent a rebreathing as well as a hyperventilation.

RESULTS

At rest, (Equation is included in full-text article.)was 33.6 (SD 3.1) mmHg. At rebreathing, MCAv increased at 38 mmHg (Equation is included in full-text article.), MAP - at 43 mmHg (Equation is included in full-text article.). By hyperventilation, MCAv decreased at 28 mmHg (Equation is included in full-text article.), MAP - at 26 mmHg (Equation is included in full-text article.). When (Equation is included in full-text article.)reached 43 mmHg, (Equation is included in full-text article.)increased from 2.3 (SD 1.4) to 3.3 (SD 1.2)%/mmHg (P<0.01). When (Equation is included in full-text article.)decreased to 26 mmHg, (Equation is included in full-text article.)increased from -3.6 (SD 2.5) to -5.9 (SD 3.9)%/mmHg (P<0.01).

CONCLUSION

Within the alteration of (Equation is included in full-text article.)above 43 and under 26 mmHg, BP increased and decreased, respectively, leading to a change in (Equation is included in full-text article.).