Peripheral Resistance Baroreflex During Incremental Bicycle Ergometer Exercise: Characterization and Correlation With Cardiac Baroreflex

The arm of the baroreflex (BR) controlling peripheral resistances (PR), labeled as BR of PR (prBR), was characterized through an extension of the cardiac BR (cBR) sequence analysis. The method exploits recordings of skin blood flow (SBF) from the palm of the non-dominant hand via a laser Doppler flowmeter and of arterial pressure (AP) from the middle finger of the same hand via a plethysmographic device. PR was estimated beat-by-beat as the ratio of mean AP to mean SBF computed over the same heart period (HP). Peripheral resistances-diastolic arterial pressure (PR-DAP) sequences featuring simultaneous increases of PR and decreases of diastolic AP (DAP) or vice versa were identified and the slope of the regression line in the (DAP, PR) plane was taken as an estimate of prBR sensitivity (BRS prBR ). The percentage of prBR sequences (SEQ% prBR ) was taken as a measure of prBR involvement and the prBR effectiveness index (EI prBR ) was computed as the fraction of DAP sequences capable to drive antiparallel PR variations. Analogous markers were computed over cBR from HP and systolic AP (SAP) variability [i.e., cBR sensitivity (BRS cBR ), percentage of cBR sequences (SEQ% cBR ) , and effectiveness index of the cBR (EI cBR )]. prBR and cBR were typified during incremental light-to-moderate bicycle ergometer exercise at 10, 20, and 30% of the maximum effort in 16 healthy subjects (aged from 22 to 58 years, six males). We found that: (i) BRS cBR decreased gradually with the challenge, while BRS prBR declined only at the heaviest workload; (ii) SEQ% cBR decreased solely at the lightest workload, while the decline of SEQ% prBR was significant regardless of the intensity of the challenge; (iii) EI prBR and EI cBR were not affected by exercise; (iv) after pooling together all the data regardless of the experimental conditions, BRS prBR and BRS cBR were uncorrelated, while SEQ% cBR and SEQ% prBR as well as EI cBR and EI prBR , were significantly and positively correlated; (v) when the correlation between SEQ% cBR and SEQ% prBR and between EI cBR and EI prBR was assessed separately in each experimental condition, it was not systematically detected. This study suggests that prBR characterization provides information complementary to cBR that might be fruitfully exploited to improve patients’ risk stratification.