Cardiol Res

Cardiology Research, ISSN 1923-2829 print, 1923-2837 online, Open Access

Article copyright, the authors; Journal compilation copyright, Cardiol Res and Elmer Press Inc

Journal website https://www.cardiologyres.org

Original Article

Volume 15, Number 1, February 2024, pages 29-36

Partial Pressure of End-Tidal Oxygen and Blood Lactate During Cardiopulmonary Exercise Testing in Healthy Older Participants and Patients at Risk of Cardiac Disease

Figure 1. Relationship between ΔPETO₂, ΔETO₂, and BLa. The diamond (◊) and dotted line indicates healthy subjects, and the circle (○) and straight line indicate patients with cardiac risks. ΔPETO₂ and ΔETO₂ were not correlated with BLa from rest to VAT (BLa (VAT - rest)) in both groups (a, b). In subjects at risk for cardiac disease, ΔPETO₂ from rest to VAT (ΔPETO₂) showed a significant correlation with the increase in BLa from rest to peak (ΔBLa (peak - rest)) (c). ΔPETO₂ and the increase in BLa from VAT to peak (ΔBLa (peak - VAT)) also showed a significant correlation (e). ΔETO₂ also showed similar associations (d, f). ETO₂: end-tidal oxygen concentration; PETO₂: partial pressure of end-tidal oxygen; BLa: blood lactate; VAT: ventilatory anaerobic threshold.

**Table 1.** Data of Participants’ Clinical Characteristics
Characteristics	Healthy group (H: n = 22)	Patient group (P: n = 11)	P value
Data are presented as mean ± standard deviation (SD) and 95% confidence intervals, and obesity was defined as BMI > 25 kg/m². No significant differences in clinical characteristics, such as age and BMI, were observed between the two groups. H: healthy group; P: patients group; CTR: cardiothoracic ratio; BMI: body mass index; BNP: brain natriuretic peptide; eGFR: estimated glomerular filtration rate; Hb: hemoglobin; Ht: hematocrit; LVEF: left ventricular ejection fraction; CCB: calcium channel blocker; ACEI: angiotensin-converting enzyme inhibitor; ARB: angiotensin II receptor blockers; DPP-4: dipeptidyl peptidase-4; SGLT2: sodium glucose cotransporter 2; NS: not significant; M: male; F: female.
Age, years	69.6 ± 6.6	72.6 ± 8.5	NS
	66.8 - 72.4	67.6 - 77.6
Sex	M: 9, F: 13	M: 9, F: 2	NS
Height, cm	158.5 ± 6.4	164.8 ± 3.6	0.005
	155.9 - 161.2	162.7 - 167.0
Body weight, kg	56.0 ± 8.4	66.1 ± 10.5	0.005
	52.5 - 59.5	59.9 - 72.3
BMI, kg/m²	22.2 ± 2.1	24.4 ± 4.1	NS
	21.3 - 23.1	21.9 - 26.8
CTR, %		48.6 ± 4.3
		45.1 - 50.7
BNP, pg/dL		79.8 ± 131.6
		-0.8 - 148.6
eGFR, mL/min/1.73 m²		63.7 ± 16.5
		54.0 - 73.5
Hb, g/dL		13.8 ± 0.9
		13.2 - 14.3
Ht, %		41.7 ± 2.6
		40.1 - 43.2
LVEF, %		68.3 ± 14.1
		60.2 - 76.0
Comorbidity
Hypertension, n (%)	0 (0)	11 (100)
Dyslipidemia, n (%)	0 (0)	8 (73)
Impaired glucose tolerance, n (%)	0 (0)	2 (18)
Obesity, n (%)	2 (9)	4 (36)
Medication
CCB, n (%)	0 (0)	7 (63.6)
ACEI/ARB, n (%)	0 (0)	5 (45.5)
Beta blocker, n (%)	0 (0)	3 (27.3)
Statin, n (%)	0 (0)	6 (54.5)
Antilipidemic, n (%)	0 (0)	3 (27.3)
Nitrate, n (%)	0 (0)	3 (27.3)
Antiplatelet, n (%)	0 (0)	6 (54.5)
Anticoagulant, n (%)	0 (0)	2 (18.2)
DPP-4 inhibitor, n (%)	0 (0)	2 (18.2)
SGLT2 inhibitor, n (%)	0 (0)	1 (9.1)

Table 1. Data of Participants’ Clinical Characteristics

Characteristics

Healthy group (H: n = 22)

Patient group (P: n = 11)

P value

Data are presented as mean ± standard deviation (SD) and 95% confidence intervals, and obesity was defined as BMI > 25 kg/m². No significant differences in clinical characteristics, such as age and BMI, were observed between the two groups. H: healthy group; P: patients group; CTR: cardiothoracic ratio; BMI: body mass index; BNP: brain natriuretic peptide; eGFR: estimated glomerular filtration rate; Hb: hemoglobin; Ht: hematocrit; LVEF: left ventricular ejection fraction; CCB: calcium channel blocker; ACEI: angiotensin-converting enzyme inhibitor; ARB: angiotensin II receptor blockers; DPP-4: dipeptidyl peptidase-4; SGLT2: sodium glucose cotransporter 2; NS: not significant; M: male; F: female.

Age, years

69.6 ± 6.6

72.6 ± 8.5

66.8 - 72.4

67.6 - 77.6

Sex

M: 9, F: 13

M: 9, F: 2

Height, cm

158.5 ± 6.4

164.8 ± 3.6

0.005

155.9 - 161.2

162.7 - 167.0

Body weight, kg

56.0 ± 8.4

66.1 ± 10.5

0.005

52.5 - 59.5

59.9 - 72.3

BMI, kg/m²

22.2 ± 2.1

24.4 ± 4.1

21.3 - 23.1

21.9 - 26.8

CTR, %

48.6 ± 4.3

45.1 - 50.7

BNP, pg/dL

79.8 ± 131.6

-0.8 - 148.6

eGFR, mL/min/1.73 m²

63.7 ± 16.5

54.0 - 73.5

Hb, g/dL

13.8 ± 0.9

13.2 - 14.3

Ht, %

41.7 ± 2.6

40.1 - 43.2

LVEF, %

68.3 ± 14.1

60.2 - 76.0

Comorbidity

Hypertension, n (%)

0 (0)

11 (100)

Dyslipidemia, n (%)

0 (0)

8 (73)

Impaired glucose tolerance, n (%)

0 (0)

2 (18)

Obesity, n (%)

2 (9)

4 (36)

Medication

CCB, n (%)

0 (0)

7 (63.6)

ACEI/ARB, n (%)

0 (0)

5 (45.5)

Beta blocker, n (%)

0 (0)

3 (27.3)

Statin, n (%)

0 (0)

6 (54.5)

Antilipidemic, n (%)

0 (0)

3 (27.3)

Nitrate, n (%)

0 (0)

3 (27.3)

Antiplatelet, n (%)

0 (0)

6 (54.5)

Anticoagulant, n (%)

0 (0)

2 (18.2)

DPP-4 inhibitor, n (%)

0 (0)

2 (18.2)

SGLT2 inhibitor, n (%)

0 (0)

1 (9.1)

**Table 2.** Data of End-Tidal Oxygen Concentration and Blood Lactate in CPET
	Group	Rest	WU	VAT	RCP	Peak
^aSignificant (P < 0.05) vs. rest. ^bSignificant (P < 0.05) vs. group H. Data are presented as mean ± standard deviation (SD) and 95% confidence intervals. Both PETO₂ and ETO₂ were significantly lower at VAT compared to those at rest. In addition, in ETO₂, ETO₂ during VAT was significantly higher in the patient group than in the healthy group, and PETO₂ showed a similar trend. H: healthy group; P: patients group; VO₂: oxygen uptake; VO₂/W: oxygen uptake per weight; RER: respiratory exchange ratio; HR: heart rate; WR: work rate; ETO₂: end-tidal oxygen concentration; PETO₂: partial pressure of end-tidal oxygen; BLa: blood lactate; WU: warming-up; VAT: ventilatory anaerobic threshold; RCP: respiratory compensation point; bpm: beats per minute; CPET: cardiopulmonary exercise testing.
VO₂, mL/min	H	235 ± 41	432 ± 67^a	683 ± 131^a	1,147 ± 253^a	1,370 ± 312^a
		218 - 253	404 - 460	628 - 739	1,036 - 1,260	1,240 - 1,504
	P	248 ± 50	432 ± 99^a	678 ± 177^a	1041 ± 275^a	1,310 ± 319^a
		218 - 277	374 - 491	574 - 782	879 - 1,204	1,121 - 1,498
VO₂/W, mL/kg/min	H	4.3 ± 0.8	7.8 ± 1.4^a	12.4 ± 2.7^a	20.4 ± 3.5^a	24.5 ± 4.2^a
		3.9 - 4.6	7.2 - 8.4	11.3 - 13.6	18.9 - 22.0	22.7 - 26.3
	P	3.8 ± 0.6	6.5 ± 1.0^a	10.2 ± 1.5^a^{, b}	15.6 ± 2.3^a^{, b}	19.7 ± 3.6^a^{, b}
		3.4 - 4.1	6.0 - 7.1	9.3 - 11.1	14.2 - 16.9	17.6 - 21.8
RER	H	0.84 ± 0.07	0.85 ± 0.07	0.85 ± 0.05	1.06 ± 0.04^a	1.14 ± 0.11^a
		0.81 - 0.87	0.82 - 0.88	0.83 - 0.88	1.04 - 1.08	1.10 - 1.19
	P	0.87 ± 0.06	0.88 ± 0.08	0.87 ± 0.07	1.04 ± 0.11^a	1.16 ± 0.13^a
		0.83 - 0.90	0.83 - 0.92	0.83 - 0.92	0.98 - 1.11	1.08 - 1.25
HR, bpm	H	68.0 ± 10.6	77.5 ± 9.4^a	91.9 ± 12.6^a	121.9 ± 16.6^a	143.6 ± 19.8^a
		63.6 - 72.4	73.5 - 81.4	86.6 - 97.2	114.4 - 129.4	134.9 - 152.3
	P	66.6 ± 7.4	75.1 ± 8.7^a	86.2 ± 9.4^a	111.5 ± 15.4^a	131.5 ± 17.7^a
		62.2 - 71.0	70.0 - 80.2	80.7 - 91.8	102.5 - 120.6	121.0 - 141.9
WR, watt	H			44 ± 11	82 ± 20	102 ± 21
				39 - 48	73 - 90	93 - 111
	P			38 ± 14	75 ± 18	101 ± 23
				30 - 47	65 - 86	88 - 115
PETO₂, mm Hg	H	105.5 ± 4.8	102.6 ± 5.0^a	99.3 ± 4.6^a	105.0 ± 4.2	112.0 ± 5.6^a
		103.5 - 107.5	100.5 - 104.6	97.4 - 101.2	103.1 - 106.9	109.7 - 114.3
	P	106.3 ± 4.4	105.0 ± 5.1^b	101.1 ± 6.3^a	105.0 ± 7.7	113.2 ± 7.6^a
		103.7 - 108.9	102.0 - 108.0	97.3 - 104.8	100.4 - 109.6	108.7 - 117.7
ETO₂, %	H	15.0 ± 0.7	14.6 ± 0.7^a	14.1 ± 0.7^a	14.9 ± 0.6	15.9 ± 0.8^a
		14.7 - 15.3	14.3 - 14.9	13.8 - 14.4	14.6 - 15.2	15.6 - 16.2
	P	15.2 ± 0.6	15.0 ± 0.7^b	14.4 ± 0.9^a^{, b}	15.0 ± 1.0	16.2 ± 1.0^a
		14.8 - 15.5	14.6 - 15.4	13.9 - 14.9	14.4 - 15.6	15.6 - 16.8
Bla, mmol/L	H	1.15 ± 0.32		1.50 ± 0.28^a		5.29 ± 1.72^a
		1.02 - 1.28		1.38 - 1.62		4.57 - 6.01
	P	1.35 ± 0.29		1.79 ± 0.40^a		5.91 ± 2.48^a
		1.19 - 1.52		1.55 - 2.03		4.45 - 7.37

Table 2. Data of End-Tidal Oxygen Concentration and Blood Lactate in CPET

Group

Rest

VAT

RCP

Peak

^aSignificant (P < 0.05) vs. rest. ^bSignificant (P < 0.05) vs. group H. Data are presented as mean ± standard deviation (SD) and 95% confidence intervals. Both PETO₂ and ETO₂ were significantly lower at VAT compared to those at rest. In addition, in ETO₂, ETO₂ during VAT was significantly higher in the patient group than in the healthy group, and PETO₂ showed a similar trend. H: healthy group; P: patients group; VO₂: oxygen uptake; VO₂/W: oxygen uptake per weight; RER: respiratory exchange ratio; HR: heart rate; WR: work rate; ETO₂: end-tidal oxygen concentration; PETO₂: partial pressure of end-tidal oxygen; BLa: blood lactate; WU: warming-up; VAT: ventilatory anaerobic threshold; RCP: respiratory compensation point; bpm: beats per minute; CPET: cardiopulmonary exercise testing.

VO₂, mL/min

235 ± 41

432 ± 67^a

683 ± 131^a

1,147 ± 253^a

1,370 ± 312^a

218 - 253

404 - 460

628 - 739

1,036 - 1,260

1,240 - 1,504

248 ± 50

432 ± 99^a

678 ± 177^a

1041 ± 275^a

1,310 ± 319^a

218 - 277

374 - 491

574 - 782

879 - 1,204

1,121 - 1,498

VO₂/W, mL/kg/min

4.3 ± 0.8

7.8 ± 1.4^a

12.4 ± 2.7^a

20.4 ± 3.5^a

24.5 ± 4.2^a

3.9 - 4.6

7.2 - 8.4

11.3 - 13.6

18.9 - 22.0

22.7 - 26.3

3.8 ± 0.6

6.5 ± 1.0^a

10.2 ± 1.5^a^{, b}

15.6 ± 2.3^a^{, b}

19.7 ± 3.6^a^{, b}

3.4 - 4.1

6.0 - 7.1

9.3 - 11.1

14.2 - 16.9

17.6 - 21.8

RER

0.84 ± 0.07

0.85 ± 0.07

0.85 ± 0.05

1.06 ± 0.04^a

1.14 ± 0.11^a

0.81 - 0.87

0.82 - 0.88

0.83 - 0.88

1.04 - 1.08

1.10 - 1.19

0.87 ± 0.06

0.88 ± 0.08

0.87 ± 0.07

1.04 ± 0.11^a

1.16 ± 0.13^a

0.83 - 0.90

0.83 - 0.92

0.98 - 1.11

1.08 - 1.25

HR, bpm

68.0 ± 10.6

77.5 ± 9.4^a

91.9 ± 12.6^a

121.9 ± 16.6^a

143.6 ± 19.8^a

63.6 - 72.4

73.5 - 81.4

86.6 - 97.2

114.4 - 129.4

134.9 - 152.3

66.6 ± 7.4

75.1 ± 8.7^a

86.2 ± 9.4^a

111.5 ± 15.4^a

131.5 ± 17.7^a

62.2 - 71.0

70.0 - 80.2

80.7 - 91.8

102.5 - 120.6

121.0 - 141.9

WR, watt

44 ± 11

82 ± 20

102 ± 21

39 - 48

73 - 90

93 - 111

38 ± 14

75 ± 18

101 ± 23

30 - 47

65 - 86

88 - 115

PETO₂, mm Hg

105.5 ± 4.8

102.6 ± 5.0^a

99.3 ± 4.6^a

105.0 ± 4.2

112.0 ± 5.6^a

103.5 - 107.5

100.5 - 104.6

97.4 - 101.2

103.1 - 106.9

109.7 - 114.3

106.3 ± 4.4

105.0 ± 5.1^b

101.1 ± 6.3^a

105.0 ± 7.7

113.2 ± 7.6^a

103.7 - 108.9

102.0 - 108.0

97.3 - 104.8

100.4 - 109.6

108.7 - 117.7

ETO₂, %

15.0 ± 0.7

14.6 ± 0.7^a

14.1 ± 0.7^a

14.9 ± 0.6

15.9 ± 0.8^a

14.7 - 15.3

14.3 - 14.9

13.8 - 14.4

14.6 - 15.2

15.6 - 16.2

15.2 ± 0.6

15.0 ± 0.7^b

14.4 ± 0.9^a^{, b}

15.0 ± 1.0

16.2 ± 1.0^a

14.8 - 15.5

14.6 - 15.4

13.9 - 14.9

14.4 - 15.6

15.6 - 16.8

Bla, mmol/L

1.15 ± 0.32

1.50 ± 0.28^a

5.29 ± 1.72^a

1.02 - 1.28

1.38 - 1.62

4.57 - 6.01

1.35 ± 0.29

1.79 ± 0.40^a

5.91 ± 2.48^a

1.19 - 1.52

1.55 - 2.03

4.45 - 7.37