Disappearance of isocapnic buffering period during increasing work rate exercise at high altitude.
BACKGROUND
At sea level, ventilation kinetics are characterized during a ramp exercise by three progressively steeper slopes, the first from the beginning of exercise to anaerobic threshold, the second from anaerobic threshold to respiratory compensation point, and the third from respiratory compensation point to peak exercise. In the second ventilation phase, body CO2 stores are used to buffer acidosis owing to lactate production; it has been suggested that this extra CO2 production drives the ventilation increase. At high altitude, ventilation increases owing to hypoxia. We hypothesize that ventilation increase reduces body CO2 stores affecting ventilation kinetics during exercise.


METHODS
In eight healthy participants, we studied the ventilation kinetics during an exercise performed at sea level and at high altitude (4559 m).


METHODS
We used 30 W/2 min step incremental protocol both at sea level and high altitude. Tests were done on a cyclo-ergometer with breath-by-breath ventilation and inspiratory and expiratory gas measurements. We evaluated cardiopulmonary data at anaerobic threshold, respiratory compensation point, peak exercise and the VE/VCO2 slope.


RESULTS
At high altitude: (a) peak VO2 decreased from 2595+/-705 to 1745+/-545 ml/min (P<0.001); (b) efficiency of ventilation decreased (VE/VCO2 slope from 25+/-2 to 38+/-4, P<0.0001); (c) at each exercise step end-tidal pressure change for CO2 was lower; and (d) the isocapnic buffering period disappeared in seven over eight participants and was significantly shortened in the remaining participant.


CONCLUSIONS
Exercise performed at high altitude is characterized by two, instead of three, ventilation slopes.
Centro Cardiologico Monzino, IRCCS, Institute of Cardiology, University of Milan, and Department of Cardiology, S. Luca Hospital, Istituto Auxologico Italiano, Milan, Italy. piergiuseppe.agostoni@unimi.it
Piergiuseppe
P
Agostoni
Mariaconsuelo
M
Valentini
Damiano
D
Magrí
Miriam
M
Revera
Gianluca
G
Caldara
Francesca
F
Gregorini
Grzegorz
G
Bilo
Katarzyna
K
Styczkiewicz
Giulio
G
Savia
Gianfranco
G
Parati
D000328:Adult; D000531:Altitude; D015308:Anaerobic Threshold / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D006801:Humans; D016857:Hypocapnia / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D012123:Pulmonary Ventilation / Q000502:physiology*; D012016:Reference Values; D016897:Respiratory Burst / Q000502:physiology*