Estimation of the ventilatory compensation point by the minute ventilation and heart rate relationship during exercise at high altitude

We previously demonstrated that changes in the slope (S) of increment in minute ventilation over heart rate (ΔV9E/ΔHR) can be utilized for the detection of the ventilatory compensation point (VCP) during incremental exercise at sea level (SL) (Onorati P, EurJApplPhysiol, 2008). We hypothesized that the influence of hypoxic conditions, such as at high altitude (HA), on the V9E and HR responses do not compromises VCP detection using the ΔV9E/ΔHR method. Methods: Six healthy subjects (42±14SD,yrs) performed, on immediate ascent to HA (5050m) and at sea level (SL) a maximal-incremental exercise test on cycle ergometer; O 2 uptake (V9O 2 ), CO 2 output (V9CO 2 ), V9E and HR were measured breath-by-breath. The ΔV9E/ΔHR method was compared to standard one (ΔV9E/ΔV9CO 2 ). The S of ΔV9E/ΔHR, before (S1) and after (S2) VCP were computed by linear regression. Results: A significant difference in the slope of increase in ΔV9E/ΔHR, S1 vs S2, was observed both at SL and HA, as well as a good agreement (mean difference ± 2SD of the differences) between methods (ΔV9E/ΔHR vs ΔV9E/ΔV9CO 2 ) in VCP detection was found in both environmental conditions (SL: -22±112 V9O 2 ml and HA: 39±81 V9O 2 ml). For both methods, V9O 2 value at VCP (VCP-V9O 2 ) was significantly lower at HA compared to SL while, whereas S1 and S2 were significantly higher at HA compared to SL. Conclusions: The changes in the ΔV9E/ΔHR slope during cycle ergometer incremental exercise can be used for VCP detection alternately to the ventilatory equivalents method despite the environmental conditions (hypoxic vs normoxic) which, however, significantly affect the S and VCP-V9O 2 values.