1.

Introduction

The jugular veins are critical drainage pathways from the head to the heart, with important implications for both cerebral and cardiac health. Cerebral blood drains primarily through the internal jugular veins (IJV) in the majority of healthy individuals in a supine position,¹ although the drainage pathway is dependent on posture and central venous pressure (CVP).² Impeded venous return may be reflective of underlying cardiovascular pathology affecting venous return to the right atrium and may contribute to detrimental long-term effects in cerebral and intracranial health.^3–6 Thus, assessing jugular venous status may provide insight into cardiac function and cerebral drainage.

Due to the IJV’s high compliance and close proximity to the heart, jugular vein hemodynamics reflect cardiac function and right atrial hemodynamics. In heart failure, the examination of the jugular venous pulse is considered to be one of the most important physical markers for determining a patient’s fluid status.^7,8 However, accurate physical examination of the jugular venous pulse is challenging and highly dependent on clinical experience.^9,10 Recent studies have investigated the link between jugular vein distention, measured with ultrasound, and congestion.^11,12 The ratio of the IJV size, measured as either a cross-sectional area (CSA) or diameter, between baseline and peak Valsalva strain using ultrasound has been proposed for determining congestion and right atrial status in heart failure.^13,14 IJV compliance, which describes the vein’s passive volume response to a change in transmural pressure, may provide additional insight into cardiovascular function. Venous compliance traditionally relies on monitoring the vessel size as a function of distending pressure. In the limbs, a strain gauge measures tissue volume changes and cannot localize single vessels. Ultrasound can measure the cross-sectional vessel area or 3D vessel reconstruction in large vessels, but extreme care needs to be taken by a trained technician to avoid artificially altering the transmural pressure through probe pressure.

Optical technologies have been proposed for monitoring changes in jugular blood volume. Wearable and noncontact optical biosensors have been developed to monitor the jugular venous pulse at various parts of the neck. Reflectance pulse oximeters are able to monitor the jugular venous pulse waveform from the anterior neck.¹⁵ Additionally, near-infrared spectroscopy sensors placed on the lateral neck at the location of the external jugular vein have been shown to predict right atrial pressure and outpatient heart failure risk.¹⁶ Our previous work has shown that changes in optical attenuation of the jugular vein correlate with changes in CVP within the linear range.¹⁷ Optical technologies provide a promising approach to nonintrusively monitoring changes in jugular vein volume, but they have not been investigated for quantifying jugular compliance across a wide range of pressures.

In this paper, we sought to quantify the jugular venous compliance curve by relating changes in the vessel size, using noncontact optical hemodynamic imaging, to CVP from antecubital cannulation across a wide range of pressures. We hypothesized that optical attenuation from the jugular vein would reflect the underlying vessel size across the nonlinear range of pressure values, which was evaluated using a graded Valsalva maneuver to increase intrathoracic pressure and thus CVP.

2.

Methods

3.

Results

Figure 1 shows the group responses of CVP, CSA, and JVA to the graded Valsalva protocol. During the Valsalva strain, CSA and JVA increased with CVP. Four-beat average JVA and CSA were strongly correlated (median and interquartile range) across all participants [$r=0.986$, (0.983, 0.987)] (Fig. 2).

Fig. 1

Group responses to the graded Valsalva maneuver. Stepwise (per 2 s) increases of 2 mmHg in mouth pressure translated to progressive increases in CVP, IJV CSA, and optical JVA relative to baseline. Dashed lines represent the start/stop of Valsalva strain. Shaded areas represent $\pm \mathrm{SD}$.

Table 1

Cardiovascular variables assessed at rest and peak Valsalva strain while supine.

Fig. 2

Individual correlation plots between IJV CSA and JVA four-beat averages across the graded Valsalva maneuver.

Systemic and local cardiovascular variables were significantly altered at peak Valsalva strain compared with resting supine baseline (Table 1). CVP more than doubled on average between baseline and peak strain ($10.7\pm 4.4$ vs. $25.8\pm 5.4{\mathrm{cmH}}_2\mathrm{O}$; $p<0.01$). This combined with a 31% mean reduction in SV indicated impeded venous return, with commensurate increases in both CSA ($0.4\pm 0.2$ vs. $1.1\pm 0.3{\mathrm{cm}}^2$; $p<0.01$) and JVA ($0.78\pm 0.29$ vs. $0.85\pm 0.30\text{a}\mathrm{.}\text{u}\mathrm{.}$; $p<0.01$). SV was reduced ($81\pm 14$ vs. $55\pm 13\mathrm{mL}$; $p<0.01$), and despite an increase in HR ($67.9\pm 12.8$ vs. $79.7\pm 17.9\mathrm{beats}{\min }^{-1}$; $p=0.04$), cardiac output fell ($5.4\pm 1.1$ vs. $4.2\pm 0.7\mathrm{L}{\min }^{-1}$; $p<0.01$). MAP increased significantly, and although the mean cerebral blood velocity was unchanged across the sample, the cerebral blood velocity increased in five of eight participants (Fig. 3; see Sec. 4).

Fig. 3

Individual data showing changes in cardiovascular variables from supine baseline to peak Valsalva strain at 20 mmHg. Arterial and CVPs, as well as jugular venous volume measurements, significantly increased from baseline to peak strain, with a commensurate decrease in cardiac output (see Table 1 for statistical analyses). Error bars represent $\pm \mathrm{SD}$.

Individual pressure-volume curves show a logarithmic relationship between pressure and volume in both CSA and JVA data [Fig. 4(a)], indicating a nonlinear reduction in compliance as pressure increased. Baseline CVP ranged from 5.7 to $17.9{\mathrm{cmH}}_2\mathrm{O}$. Figure 5 shows individual compliance curves derived from each participant’s pressure-volume curves. As CVP increased, both JVA-derived ($C_{\mathrm{JVA}}$) and CSA-derived ($C_{\mathrm{CSA}}$) compliance decreased, and the rate of decrease was reduced at higher pressures. The data demonstrate large changes in volume for small changes in pressure at the initial low pressures [$C_{\mathrm{JVA}}:(8.1\pm 7.1)\times {10}^{-3}\mathrm{a}.\mathrm{u}.{\mathrm{cm}\text{H}}_2{\mathrm{O}}^{-1}$; $C_{\mathrm{CSA}}:(8.4\pm 7.3)\times {10}^{-2}{\mathrm{cm}}^2{\mathrm{cmH}}_2{\mathrm{O}}^{-1}$], and a slowed reduction in compliance at high pressures as the vein converged toward maximal distention [$C_{\mathrm{JVA}}:(3.1\pm 0.1)\times {10}^{-3}\mathrm{a}.\mathrm{u}.{\mathrm{cmH}}_2{\mathrm{O}}^{-1}$; $C_{\mathrm{CSA}}:(2.4\pm 0.8)\times {10}^{-2}{\mathrm{cm}}^2{\mathrm{cmH}}_2{\mathrm{O}}^{-1}$], resulting in median compliance reduction of 49% and 56%, respectively [Fig. 4(b)]. The percent reduction in compliance between methods were not significantly different ($Z=-1.24$, $p=0.21$).

Fig. 4

Individual pressure-volume curves (a) and compliance changes (b) during graded Valsalva from 0 to 20 mmHg over 20 s, using IJV CSA (top row) and normalized JVA (bottom row) as proxies for changes in vessel volume.

Fig. 5

Individual compliance curves calculated from each participant’s pressure-volume curves using both JVA (black) and IJV CSA (blue) as proxies for vessel volume. Compliance decreased as CVP increased during the graded Valsalva maneuver. Each point represents a four-beat average during the graded Valsalva maneuver.

In the case with the lowest resting CVP (P7, bottom left panel in Fig. 5), a rapid initial drop in compliance was observed, indicating a very compliant vessel at baseline. Note that the y-axis for this participant was increased to accommodate the initial high compliance.

4.

Discussion

In this study, we applied a progressive increase in intrathoracic pressure through a Valsalva maneuver to gain insight into jugular vein distension and compliance. Previous studies have proposed ultrasound metrics of vessel size changes from baseline to peak of a Valsalva maneuver to determine congestion and right atrial status in heart failure.^13,14 A smaller increase in the diameter is a direct consequence of elevated right atrial pressure with an already partially distended jugular vein during rest. Our data, obtained in healthy young adults, showed that JVA by optical imaging can be an accessible noncontact alternative to ultrasound for assessing jugular vein compliance, in conjunction with pressure measurements, and right heart status. The compliance curves derived from JVA may provide additional insight into venous status using a controlled graded intrathoracic pressure change. This study was conducted on young healthy adults to evaluate compliance curves using JVA and CVP, and it confirmed expected decreases in compliance at higher venous pressures. Clinical evaluation of jugular distention using JVA alone may provide relevant measurements related to right atrial pressure,^13,14 without requiring pressure monitoring.

We observed a strong linear correlation between CSA and JVA, indicating that JVA tracked changes in volume well when considering CSA to be a proxy for vessel volume and expanding on our previous findings that JVA tracks changes in CVP within the linear range,¹⁷ as well as CSA across head-down tilt and lower body negative pressure provocations.²⁵ Calculating compliance using CSA (cross-sectional compliance²⁶) assumes that changes in vessel volumes and vessel diameters are linearly correlated. By calculating compliance at a particular location along the jugular track, we demonstrated that optical imaging provides nonintrusive jugular venous assessment for a unit vessel length. As the IJV has a variable shape along the length of the vessel,²⁷ expanding this analysis across the length of the neck may further advance insights into longitudinal distention and filling patterns.

Since JVA is a measure of optical attenuation, which is expressed in arbitrary units, $C_{\mathrm{JVA}}$ is expressed in $\mathrm{a}.\mathrm{u}{.\mathrm{cm}\text{H}}_2{\mathrm{O}}^{-1}$. Although we have observed a strong linear correlation between JVA and CSA across pressures and general agreement between $C_{\mathrm{CSA}}$ and $C_{\mathrm{JVA}}$, it becomes challenging to compare compliance values between individuals due to differences in endogenous tissue chromophores and scattering agents.²⁸ However, the ratio between maximum the jugular vein diameter during Valsalva to the diameter at rest, and the not maximum jugular vein diameter alone, was found to be a significant risk factor for heart failure hospitalization or mortality.¹³ Thus, in the context of right atrial screening, tracking changes within an individual is more important than comparing absolute compliance values between individuals.

Compliance changes when CVP was above $20{\mathrm{cmH}}_2\mathrm{O}$ (14.7 mmHg) were marginal across participants that attained this pressure. In our protocol, participants performed the Valsalva while supine; thus there were no hydrostatic effects between the jugular vein and the heart, so CVP reflected right atrial pressures. This observed effect is consistent with clinical guidelines on assessing congestion thresholds, which define elevated congestion at 15 mmHg ($20.4{\mathrm{cmH}}_2\mathrm{O}$) in transthoracic echocardiography and pulmonary hypertension.^29,30 Patients with small jugular vein diameter ratios in a Valsalva maneuver are more likely to have signs of congestion.¹³ Further investigations are needed to determine whether this asymptotic compliance pattern may be suitable for assessing congestion in clinical populations.

Increased MAP, CVP, and cerebral blood velocity in seven of nine participants suggests that intracranial pressure increased from baseline to peak Valsalva, consistent with previous findings.³¹ Venous outflow is an important contributor to intracranial pressure regulation.³² Paired with MAP, changes in JVA may indicate impaired cerebral drainage secondary to elevated CVP. Although the Valsalva maneuver provides a convenient way to assess acute pressure-induced sympathoexcitatory response while increasing right atrial pressure, further investigations are needed to assess the feasibility of longitudinal monitoring of cerebral drainage for applications such as monitoring intracranial hypertension³³ and remodeling of the eye in spaceflight.^5,6

Although individual compliance curves showed a general decrease in compliance as CVP increased, a transient rise in $C_{\mathrm{CSA}}$ was observed at low pressures ($\sim 15{\mathrm{cmH}}_2\mathrm{O}$) in some participants. This was not observed in the corresponding $C_{\mathrm{JVA}}$ curves, and after these initial pressures, $C_{\mathrm{CSA}}$ and $C_{\mathrm{JVA}}$ curves matched each other. Given these empirical observations, these observed transient increases may have been a result of small ultrasound probe hold-down pressure restricting vessel distention at low CVP. At $15{\mathrm{cmH}}_2\mathrm{O}$ (11 mmHg), a probe pressure of $0.15\mathrm{N}{\mathrm{cm}}^{-2}$ (0.21 psi) is sufficient for collapsing the jugular vein. This provides motivation for noncontact approaches for quantifying vessel distention when low pressures are of interest.

We observed a decrease in MAP from baseline to peak Valsalva strain in one female participant (P7 in figures above). Consequently, the mean cerebral blood velocity decreased. This participant had the lowest resting CVP and fastest initial change in compliance, experienced transient symptoms (hearing disturbance and lightheadedness) during a separate expiratory effort of 40 mmHg and extremity numbness during $-40\mathrm{mmHg}$ lower body negative pressure (data not shown), and did not consume food or water for at least 8 h before arriving at the lab, despite the instructions to consume 1 L of water prior to the study. We therefore hypothesize that the participant was hypovolemic, causing low cardiac filling pressures and plasma volume, which has been associated with marked reductions in arterial blood pressure during Valsalva strain.³⁴

Noncontact optical monitoring of the jugular vein may provide new ways for assessing cardiovascular health in individuals affected by changes in fluid status, such as in heart failure, sepsis, and spaceflight. Clinically relevant jugular physiology, such as distention^7,35 and stasis,³⁶ is often difficult to discern visually.^9,10 Volume-related biomarkers are less susceptible to cardiovascular compensatory mechanisms and thus may provide earlier detection of fluid-related pathophysiology.³⁷ Optical assessment of jugular venous compliance may be helpful in identifying jugular venous abnormalities secondary to changes in cardiac and fluid status.

There are limitations to this study. The sample size was small; thus group statistics may not be appropriate for other populations. The participants were healthy young adults; thus further studies are needed to investigate jugular venous dynamics in other populations (e.g., clinical, obese, or older adults and pediatrics). As this was a feasibility study, measurement repeatability should be explicitly evaluated.

5.

Conclusion

We investigated the feasibility of assessing dynamic jugular venous compliance using noncontact optical imaging measures of vessel volume changes in a healthy young adult sample. Compliance was calculated over a range of pressures attained by modulating the intrathoracic pressure through a graded Valsalva maneuver. JVA (optical) was compared with IJV CSA (ultrasound) as vessel volume proxies for calculating pressure-volume and compliance data. Changes in JVA and CSA were strongly correlated during graded Valsalva across participants. JVA significantly increased between baseline and peak strain, with a commensurate significant increase in CSA and CVP. Pressure-volume curves, using JVA and CSA as proxies for vessel volume, showed logarithmic volume responses as pressure increased. Both JVA- and CSA-derived compliance decreased as pressure increased, with a slowed reduction at high pressures as the vein converged toward maximal distention. These results showed that JVA was able to quantify changes in IJV volume without the potential for compression at low venous pressures. Taken together, these results show promise for using noncontact optical imaging to assess dynamic changes in vessel volume for evaluating congestion in heart failure and venous biomarkers secondary to altered cardiac and fluid status.