Respiratory timing during exercise

The respiratory compensation point (RCP) is the point during incremental
exercise at which the ventilation suddenly increases in response to lactic
acidosis. This is visible as a sudden decrease in partial pressure of carbon
dioxide (pCO2) in arterial blood. It is remarkable that there is usually a
delay between the onset of lactic acidosis and this respiratory response. This
delay is called the *isocapnic buffering phase. The mechanism that is
responsible for the RCP is unclear.
RCP is an important factor in the development of dyspnoea during exercise.
Dyspnoea is the most important complaint of patients with cardiopulmonary
disease. For instance, shortness of breath has a major impact on exercise
capacity and quality of life in patients with chronic obstructive pulmonary
disease (COPD)(3). However, in many patients the nature of ventilatory
limitation during exercise is also unclear.
To shed more light on the mechanism of the ventilatory response during exercise
we applied the analysis of breath-to-breath respiratory variability. In healthy
subjects this type of analysis provided insights into the respiratory control
system.
Analysis of breath-to-breath respiratory variability may provide more
information about the mechanism of the respiratory compensation point.
Preliminary data of a small cohort of nine healthy subjects showed that after
the RCP the breath-to-breath variability of tidal volume (VT), inspiratory time
(TI) and expiratory time (TE) is reduced. These data also showed that, after
the RCP, TI and TE are tightly coupled.
An extension of this analysis will improve the knowledge about the regulatory
mechanisms of respiration during exercise and tachypnoea as a cause of the
shortness of breath that patients experience during exercise.
An incremental exercise test is a useful non-invasive diagnostic tool to assess
the ventilatory mechanisms during exercise. Therefore, more knowledge about
these mechanisms improves the diagnostic power of the incremental exercise test
and will prevent the patient from further, more invasive diagnostic tests.
Our main objective is to improve the understanding of the respiratory
compensation point during exercise. To this end we applied the analysis the
breath-to-breath respiratory variability after the RCP in a group of healthy,
well trained subjects during an incremental exercise test.

2.1 Primary Objective(s):
The primary objective of this study is to determine whether analysis of
breath-to-breath respiratory variability provides more information on the
mechanism that is responsible for the RCP.
Two hypotheses are tested:
1. After RCP the breath-to-breath variability of VT, TI and TE is reduced.
2. After RCP there is a tight coupling between TI and TE.

2.2 Secondary Objective(s):
The secondary objectives of this study are to determine the RCP, and the timing
of the anaerobic threshold (AT) and lactic acidosis in relationship to the RCP.

This study will be set up as a prospective, observational study. Eligible
participants will be sought at recreational cycle clubs and approached by the
investigators orally or by advertisement.
An incremental exercise test will be performed in all subjects.
This study will be conducted in the hospital of the Noordwest Ziekenhuisgroep,
location Alkmaar.

The subjects will be asked for a day to be present in the North West Group
Hospital, location Alkmaar. During this day there is a short history, physical
examination, and the screenings tests will be performed; a venipuncture, ECG
and spirometry. If a subject is found to be suitable for participation a
incremental exercise test is carried out with an radial artery puncture twice.

Risks
Venipuncture: local hematoma
Radial artery puncture: local hematoma, arterial spasm, local hematoma,
fainting or a vasovagal response.
The risks are small, because the punctures are performed by experienced
analysts. The damage wich could occur is reversible.

Subjects receive a report of the incremental exercise test; thus they gain
insight into their overall fitness and performance