Resting Dead Space Fraction as Related to Clinical Characteristics, Lung Function, and Gas Exchange in Male Patients with Chronic Obstructive Pulmonary Disease

Figures & data

Table 1 Demographic Data, Symptom Score, Blood Tests, Chest Radiography, and Echocardiography (n = 46)

	n	Mean	SD
Age, year	46	65.2	5.8
Height, cm	46	165.0	6.4
Weight, kg	46	60.4	11.2
Body mass index, kg/m^2	46	22.12	3.53
Smoke, py	46	42.3	19.2
OCD, cm	46	7.0	1.4
Triceps, mm	44	6.4	2.6
Mid-arm, cm	44	27.3	3.4
Borg, A.U.	46	0.05	0.19
Hemoglobin, g/dL	46	14.8	1.5
Albumin, g/dL	40	4.2	0.4
GPT, IU/L	40	21.1	16.8
Bilirubin, direct, mg/dL	42	0.25	0.29
Creatinine, mg/dL	42	1.09	0.20
Na^+, mmol/L	41	140.5	2.4
K^+, mmol/L	40	4.3	0.5
Sugar, mg/dL	41	98.8	14.7
Cholesterol, mg/dL	43	182.2	36.6
Hila-thoracic ratio	44	0.36	0.04
Cardiac-thoracic ratio	41	0.44	0.06
ADPA, cm	46	1.62	0.33
Apical 4 EDRV, cm^2	42	13.5	3.7
Apical 4 ESRV, cm^2	42	7.8	1.8
Subcostal 4 EDRV, cm^2	42	14.2	3.3
Subcostal 4 ESRV, cm^2	42	7.6	2.1
Right ventricle wall, mm	42	6.0	2.0

Abbreviations: A.U., absolute unit, ADPA: anterior descending pulmonary artery of the right lung, apical four chamber view, end-diastolic right ventricle area (EDRV), end-systolic right-ventricle area (ESRV); subcostal four-chamber view; long and short axes view: the right ventricle free wall thickness at an end-diastolic phase between the tricuspid annulus and the papillary muscle.

Table 2 Lung Function

Variables		n	Mean	SD
Total lung capacity, TLC, L		46	6.5	1.0
TLCpred, %		46	135	21
Functional residual capacity, FRC, L		46	4.8	1.0
FRCpred, %		46	162	34
Inspiratory capacity, L		46	1.7	0.5
Residual volume, RV, L		46	3.8	0.9
RV/TLC, %		46	58	9
DLCO, mL/min/mmHg		45	15.8	5.6
DLCOpred, %		45	69	22
Forced vital capacity, FVC, L		46	2.5	0.7
FVCpred, %		46	81	21
FEV1, L		46	1.2	0.5
FEV1pred, %		46	50	19
GOLD, I, II, II, IV, n (%)	3 (6.5), 18 (39.1), 19 (41.3), 6 (13.0)
FEV1/FVC, %		46	49	13
Slow vital capacity, SVC, L		46	2.7	0.7
SVCpred, %		46	89	22
MIP, cmH2O		43	68.4	18.6
MEP, cmH2O		43	103.7	22.6
PEFR, L/sec		46	2.9	1.3
PEFRpred, %		46	42	20

Abbreviations: D_LCO, the diffusion capacity of the lungs for carbon monoxide; FEV_1, forced expiratory volume in one second; GOLD I-IV, global initiative for chronic obstructive lung disease stages; MIP, maximal inspiratory pressure; MEP, maximum expiratory pressure; PEFR, peak expiratory flow rate.

Table 3 Cardiopulmonary Physiological Data, Arterial Blood Gases, Carboxyhemoglobin and Plasma Lactate Concentrations at Rest

Variables	n	Mean	SD
VO2%predicted maximum, %	46	16	3
VO2/kg, L/min/kg	46	4.1	0.8
VCO2, L/min	46	0.20	0.04
Respiratory exchange ratio	46	0.83	0.05
O2 Pulse, mL/beat	46	3.1	0.7
VE/VCO2	46	53.5	10.0
VE/VO2	46	44.5	7.4
VD/VT	45	0.58	0.08
Pa-ETCO2, mmHg	45	4.0	4.4
A-aDO2, mmHg	45	18.9	1.0
SPO2, %	45	95.3	2.6
VE, L/min	46	10.7	2.1
MVV, L/min	46	36.3	16.9
VE/MVV	46	0.35	0.16
Systolic blood pressure, mmHg	46	145.0	18.6
Diastolic blood pressure, mmHg	45	79.3	9.0
Heart rate, beat/min	46	80.6	13.2
pH	45	7.4	0.03
PaCO2, mmHg	45	40.6	6.4
PaO2, mmHg	45	79.2	10.1
HCO3^−, mEq/L	45	24.7	1.9
Carboxyhemoglobin, %	45	1.3	0.9
Methemoglobin, %	43	0.25	0.08
Lactate, mmol/L	43	1.2	0.3

Abbreviations: VO₂, oxygen uptake; VCO₂, CO₂ output; Respiratory exchange ratio, CO₂ output and oxygen uptake ratio; O₂ Pulse, oxygen uptake divided by heart rate; V_D/V_T, dead space and tidal volume ratio; P_a-ETCO₂, arterial end-tidal CO₂ pressure gradient; A-aDO₂, alveolar arterial oxygen pressure gradient; VE, minute ventilation; MVV, maximal voluntary ventilation; S_PO2, hemoglobin saturation measured by pulse oximetry.

Figure 1 Flow diagram. A total of 57 subjects with chronic obstructive pulmonary disease were screened. After excluding 10 subjects, the remaining 46 were retained for analysis after further excluding another one subject whose arterial blood gas data was not obtained.

Table 4 Comparison of Correlation Coefficient (r) Between Resting Dead Space Fraction (V_D/V_TR) and Lung Function with Variables of Interest

	n	VD/VTR	FEV1%	RV/TLC	DLCO%
		r	r	r	r
Clinical parameters
Age	45	0.30*	0.04	0.04	0.02
Height	45	-0.40**	-0.04	-0.01	-0.17
Weight	45	-0.27^¶	0.16	-0.15	0.37**
Body mass index	45	-0.12	-0.16	-0.16	0.52^†
Smoke, p-y	45	0.32*	-0.11	0.21	-0.01
OCD	45	0.08	0.34*	-0.14	0.03
Hemoglobin	45	0.29*	-0.16	-0.18	0.31*
Carboxyhemoglobin	45	0.42**	0.01	0.08	-0.16
Hila-thoracic ratio	44	0.33*	0.25^¶	-0.22	0.00
ADPA diameter	45	0.34*	-0.06	-0.11	0.13
Number of significant correlation, n		10^#	2	1	3
Lung function parameters
FRC%	45	0.02	-0.23	0.48^†	-0.24
RV/TLC	45	-0.04	-0.66^‡	1	-0.31*
DLCO%	45	0.05	0.25^¶	-0.31*	1
Slow vital capacity%	45	0.10	0.69^‡	-0.72^‡	0.12
Forced vital capacity%	45	0.02	0.75^‡	-0.64^‡	0.05
FEV1%	45	-0.01	1	-0.66^‡	0.25^¶
MIP	43	-0.19	0.13	-0.14	0.19
Post MIP	43	-0.28^¶	-0.07	-0.02	0.30^¶
Number of significant correlation, n		1^‖	4	5	3
Gas exchange parameters
PaETCO2	45	0.67^‡	-0.02	0.06	0.08
V’E/V’CO2	45	0.64^‡	0.34*	-0.19	-0.05
PaCO2	45	0.49^†	-0.32*	0.10	0.18
PaO2	45	-0.18	0.44**	-0.06	-0.08
AaDO2	45	-0.28^¶	-0.25^¶	0.02	-0.06
SPO2	45	-0.29^¶	0.12	0.08	-0.17
Number of significant correlation, n		5	4	0	0

Notes: P_aETCO₂ V’_E/V’CO₂ AaDO₂ S_aO₂. Fisher exact test was used for comparison of V_D/V_TR versus 3 lung function tests, ^# and ^‖ indicating p = 0.0001 and 0.1, respectively; ^¶Indicating modest correlation with 0.05< p 0.1, whereas ^{*, **, †, ‡}Indicating significant correlation with p <0.05, <0.01, <0.001, and <0.0001, respectively; bolded numerals highlighting a significant correlation.

Abbreviations: FEV₁, forced expired volume in one second %predicted; RV/TLC, residual volume to total lung capacity ratio; D_LCO%, diffusing capacity for carbon monoxide % predicted; p-y, packyear; OCD, oxygen cost diagram; ADPA, anterior descending pulmonary artery; FRC, functional residual capacity; SVC, slow vital capacity; MIP, maximal inspiratory capacity.

Table 5 Risk Factors of Dead Space Fraction at Rest (V_D/V_TR)

Variable	Equation	r^2	p
VD/VTRstat	1.046 (± 0.279) – 0.0042 X height (± 0.0015) + 0.0014 X smoke (± 0.0006) + 0.491 X HTR (± 0.276)	0.33	0.001
	0.942 (± 0.251) + 0.0012 X smoke (± 0.0004) + 0.0048 XVE/VCO2 (± 0.0007) – 0.472 X VTIDC (± 0.118) – 0.006 X SPO2 (± 0.0027)	0.72	< 0.0001

Notes: V_D/V_TR_stat is the V_D/V_TR obtained using multiple linear regression, smoke refers to cigarette consumption in pack-years, HTR is the hila-thoracic ratio in decimals measured from chest radiography, with the height in centimeters, and the numbers in parenthesis are standard errors.VE/VCO₂ is the ventilatory equivalent for CO₂ output, V_TIDC is the product of tidal volume in liters, inspiratory duty cycle (IDC) in decimals, and S_PO₂ is the oxyhemoglobin saturation measured with pulse oximetry. IDC is the ratio of inspiratory time of an entire respiratory cycle.