Minute ventilation and heart rate relationship for estimation of the ventilatory compensation point at high altitude: a pilot study

Background: The ventilatory compensation point (VCP) is an exercise threshold which has been used in the design of training programs in sports medicine and rehabilitation. We recently demonstrated that changes in the slope of the minute ventilation to heart rate relationship (ΔV̇ E/ΔHR) can be utilized for estimation of the VCP during incremental exercise at sea level (SL). We hypothesized that in hypoxic conditions, such as high altitude (HA), VCP can be also reliably estimated by ΔV̇ E/ΔHR.Methods: At SL and on immediate ascent to HA (5,050 m), six healthy subjects (42 ± 14 SD years) performed a maximal incremental exercise test on a cycle ergometer; O<inf>2</inf> uptake (V̇ O2), CO<inf>2</inf> output (V̇ CO2), V̇ E, and HR were measured breath-by-breath. The ΔV̇ E/ΔHR method for VCP estimation was compared to the standard method using the ventilatory equivalent for CO<inf>2</inf> (V̇ E/V̇ CO2) and end-tidal PCO<inf>2</inf> (P<inf>ET</inf>CO<inf>2</inf>). The ΔV̇ E/ΔHR slope values below (S<inf>1</inf>) and above (S<inf>2</inf>) VCP were computed by linear regression analysis.Results: A significant difference between S<inf>1</inf> and S<inf>2</inf> was observed, at SL and HA, for both the ΔV̇ E/ΔHR and V̇ E/V̇ CO2 methods for VCP estimation. A good agreement between the two methods (ΔV̇ E/ΔHR vs. V̇ E/V̇ CO2) was found for both environmental conditions; the mean difference ± 2 SD of V̇ O2 at VCP (VCP-V̇ O2) was -22 ± 112 ml/min at SL and 39 ± 81 ml/min at HA. The VCP-V̇ O2 was significantly lower at HA compared to SL; in addition, S<inf>1</inf> and S<inf>2</inf> mean values were significantly higher at HA compared to SL.Conclusion: At HA, VCP may be reliably estimated by the ΔV̇ E/ΔHR method. © 2013 Valli et al.; licensee BioMed Central Ltd.