Cardiopulmonary Testing for CTED

Eric Robbins, MD

Educational Objectives

Discuss possible exercise limitations after a complicated ICU course
Describe Fick equation and its variables that contribute to oxygen delivery
Describe features of CPET testing that would indicate ventilatory limitation to exercise
Differentiate the CPET profile of a cardiac vs. pulmonary vascular limitation to exercise
Discuss the role of invasive exercise hemodynamics

Clinical Scenario

Index Hospitalization

47M with recent hospitalization for bacterial PNA, course c/b acute bilateral PEs with shock.
Received thrombolytics.
Course further complicated by empyema, pneumothorax, and persistent air leak on his chest tube.
Intubated for 10 days.
Hospitalized for 8 weeks in total.
Discharged on a DOAC with excellent adherence.

He has a New Exercise limitation

You see at 3 months post-discharge.

Finished PT.
Exercise capacity:
- currently, 20 min daily on elliptical with significant DOE
- pre-hospital, 60+ min without dyspnea.
At home, intermittent desats to 85% with exertion.

Testing Results

PFTs

FEV1 75%, FVC 75%, FEV1/FVC 0.77

TLC 76%, DLCO 81%

MIP/MEP WNL

TTE

LV: normal size and function. normal diastology

Valves: WNL

RV: normal size and function

RVSP: ~25 mmHg, with IVC collapsing

Question 1

Part 1: In general, what mechanisms of exercise limitation might be considered in a post-ICU patient?

Generalized

Deconditioning

Neurologic

sequelae from critical illness myopathy (CIM)

Pulmonary

Restriction
Upper airway pathology
Vascular disease

Hematologic

anemia

Cardiac

residual stress-induced cardiomyopathy

Part 2: What could account for the exercise limitation in this patient?

Generalized

Deconditioning

Neurologic

sequelae from critical illness myopathy (CIM)

Pulmonary

Restriction
Upper airway pathology
Vascular disease

Hematologic

anemia

Cardiac

residual stress-induced cardiomyopathy

Question 2

Part 1: What is the incidence of exercise limitation after an episode of pulmonary embolism, and why are people limited?

Mild

50-70%, when defined as sub-maximal $VO_{2}$ on CPET

Severe

CTEPH: 4%

In Between?

CTED: 25-50% VQ defects, 20% RV dysfunction, 10% moderate to severe DOE

Question 3

State the Fick equation.

$VO_{2} = (CO) \cdot (C_{a}O_{2} - C_{v}O_{2} )$

i.e., (blood volume delivered) * (blood oxygen extracted)

Question 4

What pathophysiological processes are “packaged” within in the $AV O_{2}$ content difference term?

In other words, what categories of pathology would be taken into account by this equation?

$VO_{2} = (CO) \cdot (C_{a}O_{2} - C_{v}O_{2} )$

$= (CO) \cdot [($change in O2 content$) \cdot ($amount of blood$)]$

$= (CO) \cdot [(S_{a}O_{2} – M_{v}O_{2}) \cdot (Hgb \cdot 1.34)]$

What pathophysiological processes are “packaged” within in the $AV O_{2}$ content difference term?

$VO_2= (CO) \cdot [(S_{a}O_{2} – M_{v}O_{2}) \cdot (Hgb \cdot 1.34)]$

$S_{a}O_{2}$: lung problems (gas exchange)

$M_{v}O_{2}$: muscular utilization of oxygen & distribution of blood flow to periphery

$Hgb$: anemia, hemoglobinopathies

Question 5

What is $\frac{V_{E}}{VCO_{2}}$, conceptually?

NOTE:

$V_{E}$ = minute ventilation
$VCO_{2} \approx CO_{2}$ production

i.e., “how much minute ventilation you must perform to remove a given amount of $CO_{2}$”

i.e., how much minute ventilation is occurring per 1 L of $CO_{2}$ production

Often referred to has the ventilatory efficiency

Question 6

What CPET parameters suggest a primary cardiac limitation?

Evidence of a disproportionate HR increase to augment CO

reduced peak “$O_{2}$ pulse” (a.k.a $\frac{VO_{2}}{HR}$)

reflects reduced stroke volume (LVEF estimator)
- why: if $\uparrow VO_{2}$ but $\uparrow\uparrow HR$, $\downarrow \frac{VO_{2}}{HR}$
If you can’t augment stroke volume, you only have heart rate left!

What CPET parameters suggest a primary cardiac limitation?

low heart rate reserve

($HRR = HR_{max} - HR_{predicted}$)

$\downarrow$reduced peak $VO_{2}$
early anaerobic threshold (AT)

Question 7

Which parameters suggest a pulmonary vascular limitation to exercise?

Similar yet distinct from cardiac limitation

How PVD limitations differ from primary cardiac limitations
1. desaturation during exercise
2. elevated $\frac{V_{d}}{V_{t}}$ (physiologic dead space:tidal volume ratio)

Which parameters suggest a pulmonary vascular limitation to exercise?

elevated $\frac{V_{d}}{V_{t}}$
- that is, evidence of higher-than-expected dead space for a given tidal volume
- suggests ventilatory inefficiency ($\uparrow\frac{V_E}{VCO_2}$), but assumes patient not hyperventilating

Which parameters suggest a pulmonary vascular limitation to exercise?

NOTE: $\frac{V_{d}}{V_{t}}$ requires arterial blood to measure.

If your patient doesn’t have an arterial line placed for their CPET, computers estimate $\frac{V_{d}}{V_{t}}$ from $ETCO2

However, this assumes ventilatory inefficiency is to blame for the abnormal $\frac{V_{d}}{V_{t}}$

In lungs with significant PVD, ETCO_2 does not accurately reflect arterial values (why: increased VQ mismatch!)

Which parameters suggest a pulmonary vascular limitation to exercise?

Important

The computer value usually underestimates abnormal dead spaces in diseased lungs

Tip

If you’re concerned about PVD in a patient without direct arterial sampling during their CPET, but $\frac{V_{d}}{V_{t}}$ is only “mildly” or “moderately” elevated, that should NOT reassure you!

Question 8

Which pattern of exercise limitation is present in this patient?

measurement	patient	predicted	percent_predicted
peak VO2	1,857 mL/min	3,172 mL/min	59%
max heart rate	144	174	74%
O2 pulse	13 mL/beat	18 mL/beat	71%
lowest SpO2	80%	>95%
breathing reserve	47%	>30%
ETCO2 at AT	32
VE/VCO2	36	<33
resting Vd/Vt	0.32 (0.29	<0.4
peak Vd/Vt	0.4 (0.24	<0.25

Which pattern of exercise limitation is present in this patient?

measurement	patient	predicted	percent_predicted	interpretation
peak VO2	1,857 mL/min	3,172 mL/min	59%	he has an exercise limitation
max heart rate	144	174	74%	174 - 144 = 30, and 30 > 15, so this looks fine
O2 pulse	13 mL/beat	18 mL/beat	71%	low. SV doesn't respond appropriate to exercise; cardiac (or PVD) issue
lowest SpO2	80%	>95%		exertional desaturation is rarely cardiac related; PVD or pulmonary issue
breathing reserve	47%	>30%		he has plenty of tidal volume / minute ventilation to spare; unlikely restrictive disease
ETCO2 at AT	32			difficult to interpret, since above suggests PVD
VE/VCO2	36	<33		ventilatory inefficiency
resting Vd/Vt	0.32 (0.29	<0.4		arterial numbers show paradoxical increase in Vd/Vt; suggests PVD
peak Vd/Vt	0.4 (0.24	<0.25		ditto

Which pattern of exercise limitation is present in this patient?

Desats with exercise

$\uparrow \frac{V_d}{V_t}$

$\downarrow O_{2}$ pulse despite sufficient HRR

Conclusion: pulmonary vascular limitation!

Question 9

Does he have CTEPH?

Reminder: CTEPH requires resting pulmonary hypertension. one can have dysfunction with exertion but be “normal” at rest.

item	measurement
RA	2 mmHg
PA	27/8 (17) mmHg
PCWP	4 mmHg
tCO	6.2 L/min
PVR	2 WU

What Happens when we exercise him?

item	measurement
RA	12 mmHg
PA	100/25 (56) mmHg
PCWP	17 mmHg
tCO	15 L/min
PVR	2.6 WU

Eric Question: Does he have exercise-induced PH?

$TPR = \frac{mPAP}{CO} = \frac{56}{15} =$ 3.73

YES to eiPH!

However, we need to confirm why / how TPR increased.

Eric Question: Does he have exercise-induced PH?

$PVR = \frac{mPAP - PCWP}{CO}$

$(PVR)\cdot (CO) = mPAP - PCWP$

$(PVR)\cdot (CO) + PCWP = mPAP$

$TPR = \frac{mPAP}{CO}$

$TPR = \frac{(PVR)\cdot(CO) + PCWP}{CO}$

Eric Question: Does he have exercise-induced PH?

Note

$TPR = \frac{(PVR)\cdot(CO) + PCWP}{CO}$

So an increase in TPR can be driven by an increase in PVR or PCWP (or both)

Cutoffs: PCWP <20 mmHg or $\frac{PCWP}{CO}$ < 2 (our patient: 1.13)

Thus, exercise-induced PH from $\uparrow PVR$ is likeliest here

Question 10

Describe the normal hemodynamic response to exercise and contrast it to this patient.

steady increase in CO, mPAP, PCWP is normal

PVR mildly decreases

$TPR = \frac{mPAP}{CO}$ modestly decreases

our patient:

PVR: 2.0 $\rightarrow$ 2.6

TPR: 2.75 $\rightarrow$ 3.73

Cardiopulmonary Testing for CTED

Educational Objectives

Clinical Scenario

Index Hospitalization

He has a New Exercise limitation

Testing Results

Question 1

Part 1: In general, what mechanisms of exercise limitation might be considered in a post-ICU patient?

Part 2: What could account for the exercise limitation in this patient?

Question 2

Part 1: What is the incidence of exercise limitation after an episode of pulmonary embolism, and why are people limited?

Question 3

State the Fick equation.

Question 4

What pathophysiological processes are “packaged” within in the \(AV O_{2}\) content difference term?

What pathophysiological processes are “packaged” within in the \(AV O_{2}\) content difference term?

Question 5

What is \(\frac{V_{E}}{VCO_{2}}\), conceptually?

Question 6

What CPET parameters suggest a primary cardiac limitation?

What CPET parameters suggest a primary cardiac limitation?

Question 7

Which parameters suggest a pulmonary vascular limitation to exercise?

Which parameters suggest a pulmonary vascular limitation to exercise?

Which parameters suggest a pulmonary vascular limitation to exercise?

Which parameters suggest a pulmonary vascular limitation to exercise?

Question 8

Which pattern of exercise limitation is present in this patient?

Which pattern of exercise limitation is present in this patient?

Which pattern of exercise limitation is present in this patient?

Question 9

Does he have CTEPH?

What Happens when we exercise him?

Eric Question: Does he have exercise-induced PH?

Eric Question: Does he have exercise-induced PH?

Eric Question: Does he have exercise-induced PH?

Question 10

Describe the normal hemodynamic response to exercise and contrast it to this patient.

Question 11

Will a heart transplant improve this patient’s exercise tolerance?