Control of baboon limb blood flow and heart rate-role of skin vs. core temperature.

To discover the relative importance of body core temperature versus bodyskin temperature in raising limb blood flow and heart rate, we exposed seven unanesthetized, chaired baboons (Papio anubis) to a variety of heating protocols. First, the baboons were exposed to a 40-45 degrees C environment for 0.75-1.5 h. Arterial or right atrial blood temperature (Tbl), skin temperature (Tsk), mean right iliac blood flow (MRIF), and heart rate (HR) all increased gradually during heating. On the average, HR increased from 106 to 160 beats/min and MRIF rose to 286% of control level. To separate influences of Tbl and Tsk on cardiovascular changes, we manipulated Tbl and Tsk independently via a heat exchanger incorporated into a chronic femoral arteriovenous shunt. In most baboons, the MRIF and HR response to a hot environment could be essentially duplicated by elevation of bTbl with Tsk held neutral, while elevation of Tsk with Tbl held neutral had little effect. One baboon exhibited significant response to Tsk elevation with Tbl held neutral, although subsequent manipulation of Tbl overrode this response. We conclude that the normal response to heating in baboons is mainly attributable to drives from internal temperature-sensitive mechanisms. Elevated Tsk shows large effects only in exceptional cases.