Figures
- FIGURE 1
Graph illustrating the changes in ventilatory equivalent for carbon dioxide (described as V′E/V′CO2 in this study) in hyperventilation syndrome (HVS) suspects who are normocapnic before commencing exercise testing compared to controls. ANOVA values were used to determine significant changes in ventilatory equivalent for carbon dioxide within the groups as exercise intensity increased. **: p<0.01 compared with ventilatory equivalent for carbon dioxide at rest. V′E: minute ventilation; V′CO2: carbon dioxide production. Reproduced from [19] with permission from the publisher.
- FIGURE 2
A proposed clinical pathway for patients suspected of dysfunctional breathing, based on current practice at the Cambridge University Hospital trust. Values quoted are based on data from cited studies [19, 28, 29]. FEV1: forced expiratory volume in 1 s; VeqCO2: ventilatory equivalent for CO2; PETCO2: end-tidal carbon dioxide tension; VT: tidal volume; RR: respiratory rate.
Tables
- TABLE 1
Definitions of terms and equations used
Abbreviation Physiological parameter Significance PaCO2 Arterial carbon dioxide tension (kPa) Reflective of the concentration of CO2 in the arterial blood d Dead space volume (L) Volume of air that is inhaled that does not take part in gas exchange VT Tidal volume (L) Volume of air moved into and out of the lungs during each ventilation cycle V′E Minute ventilation (L·min−1) Volume of gas exhaled/inhaled in 1 min, equal to the VT multiplied by the RR V′CO2 Carbon dioxide production (L·min−1) d/VT Ratio of dead space volume to tidal volume A higher value indicates a larger proportion of air not engaging in gas exchange within the lungs V′E/V′CO2 Gradient of the V′E/V′CO2 slope The minute ventilation required to exhale 1 L of CO2 Equation A: 
RR Respiratory rate (min−1) Number of breaths taken per minute dsyst Dead space volume of the apparatus used (L) Volume of air that remains within the CPET apparatus e.g. breathing valve, connectors and mouth piece exterior to the mouth VeqCO2 Ventilatory equivalent for carbon dioxide Measures the efficiency of ventilation Equation B: Equation A describes the relationship of the V′E/V′CO2 slope to the physiological variables of PaCO2, d and VT. Equation B describes the relationship of VeqCO2 to the V′E, dsyst, RR and V′CO2. Definitions and significance of the relevant parameters are also described for the understanding of the presented equations CPET: cardiopulmonary exercise testing.
- TABLE 2
Relevant data from studies used to demonstrate the reviews conclusions
First author [ref.] and parameter HVS suspects Controls p-value Kinnula [28] n=10 n=10 Resting PaCO2 kPa 4.10±0.60 ND Resting pH 7.46±0.06 ND VeqCO2 at 40–50 W exercise 41.8±6.00 30.0±3.30 0.01 Jack [29] n=23 n=23 Resting PaCO2 kPa 3.87±0.60 ND VeqCO2 at 40 W exercise 38.4±5.70 28.9±2.50 ND Brat [19] n=29 n=29 Resting arterial PaCO2 kPa 4.80 (4.40–4.93) 4.80 (4.53–5.07) 0.44 Resting arterial pH 7.45 (7.43–7.47) 7.44 (7.43–7.45) 0.07 Peak exercise PaCO2 kPa 3.87±0.53 4.67±0.40 <0.01 Peak exercise arterial pH 7.47 (7.46–7.50) 7.40 (7.37–7.42) <0.01 Resting d/VT 0.21±0.11 0.22±0.10 0.77 Peak exercise d/VT 0.18±0.05 0.13±0.06 <0.01 VeqCO2 at rest 38.0 (33.0–44.0) 37.0 (32.0–40.0) 0.31 VeqCO2 at peak exercise 38.0 (35.0–43.0) 31.0 (27.0–34.0) <0.01 V′E/V′CO2 slope 37.0 (33.0–34.0) 27.0 (24.0–30.0) <0.01 Troosters [30] n=24 n=20 NQ scores 30.3±9.70 7.90±5.20 <0.001 Data are presented as mean±sd or median (interquartile range), unless otherwise stated. HVS: hyperventilation syndrome; PaCO2: arterial carbon dioxide tension; VeqCO2: ventilatory equivalent for carbon dioxide; d/VT: ratio of dead space volume to tidal volume; ND: not disclosed in study. V′E/V′CO2 slope: gradient of the V′E (abscissa) and V′CO2 (ordinate) slope; NQ: Nijmegen Questionnaire.
