Frequently Asked Questions
V̇-Com™ should be placed between the circuit tube (hose) and the interface (mask). The male end of the V̇-Com™ inserts into the 22 mm connector of the tube (hose) coming from the PAP device. The female end (22 mm) of the V̇-Com™ accepts the 22 mm connector on the mask or mask tubing.
During expiration, flow from the PAP device is the lowest during the respiratory cycle. Since the V̇-Com™ effect is flow-dependent, V̇-Com™ has minimal effect on expiratory positive airway pressure (EPAP), which is principally responsible for therapy. Expiratory upper airway resistance increases and end-expiratory pharyngeal cross-sectional area decreases in the breaths preceding a hypopnea or apnea resulting in inspiratory pharyngeal instability. EPAP overcomes this phenomenon and maintains pharyngeal patency directly from “splinting” of the airway and indirectly from the increased functional residual capacity. By maintaining EPAP, V̇-Com™ maintains therapy while providing comfort.
Before the invention of V̇-Com™, a clinician’s only option to increase comfort and initial tolerance was to decrease the pressure settings, which also decreases EPAP. This both compromises therapy and increases the risk of rebreathing CO2 from lower exhaust flow. In contrast, V̇-Com™ does not increase the risk of rebreathing CO2 because EPAP and exhaust flow are maintained. Adding V̇-Com™ to the PAP circuit is far superior to the alternative of lowering the set pressures.
The V̇-Com™ device is not therapy; it is an accessory in the PAP circuit that provides initial comfort and improves early tolerance, which is known to increase long-term adherence.
However, since beginning short trials with long-term PAP users we are finding many participants wish to keep and use their V̇-Com™ indefinitely. V̇-Com™ not only reduces inspiratory pressure and thus flow, but it “softens” the inspiratory flow curve and many patients are preferring that experience. As will be explained later, V̇-Com™ also appears to decrease unintentional leak and mouth openings which also improves the experience and possibly the therapy. There are also numerous reports that V̇-Com™ reduces the noise from the device which has led to bedpartners requesting the V̇-Com™ in the circuit.
At very high PAP settings where exhaust flow is higher than peak expiratory flow there will still be some circuit flow over the V̇-Com™ during exhalation and EPAP will decrease slightly. Certainly, by maintaining the EPAP, V̇-Com™ provides much better therapy than the alternative of reducing pressure settings.
In a small trial of 101 patients (63 on the ResMed AirSense 11, 21 on the Philips Dream Station 2, 17 on the React Health (formerly 3B Medical, Inc.) Luna 2) experiencing 4 nights without V̇-Com™ and 4 nights with the V̇-Com™, the auto-titrated pressure (P95% / P90% pressure) was unchanged (11.5 vs 11.7 cmH2O). The residual index decreased slightly but with statistical significance (p-value 0.001) (1.5 vs 1.8 events/hour), and there was significantly less leak with V̇-Com™ in the circuit (p value = <0.001). Thus, the V̇-Com™ did not decrease therapy and may improve the experience by decreasing leak.
While performing manual titration during polysomnography in 20 patients, once patients appeared to reach their therapeutic pressure, a V̇-Com™ was added to the circuit. The average pressure increase was 1.2 cmH2O and that was as expected principally at higher pressures where the higher exhaust flow can affect EPAP. It is also very possible by the design that some patients were possibly incompletely titrated before the V̇-Com™ was added.
Is “therapy” simply the maintenance of the set pressure? It is important to understand that PAP devices are designed to deliver a set pressure to the face (nose and/or mouth). This set pressure may not translate to the pharynx or lungs. The nasal valve has variable resistance depending on its anatomy and degree of congestion and can create considerable pressure drop on inspiration, affecting pharyngeal/lung pressure from nasal masks or nasal breathing on an oronasal mask. Yet, despite this pressure drop, nasal masks have been shown to require less pressure than an oronasal mask.
In addition, different interfaces have different resistances, particularly nasal pillow interfaces, which can create additional pressure drop. PAP manufacturers have attempted to account for this to some degree, but this is clearly made worse by interchanging equipment from different manufacturers. Thus, even changing the interface can affect therapy.
Breathing nasally on PAP has a totally different physiology than breathing orally. While breathing nasally drops inspiratory pressure, expiratory pressure increases because of the nasal resistance. For a nasal pillow mask, the added resistance in the pillow cushion further increases the “back” pressure or EPAP, a small cushion tremendously more than the large cushion. This is why nasal masks require less pressure to eradicate the respiratory events.
Defining “therapy” as delivering a determined pressure to the face may be an incomplete approach. The “delivered” pressure is irrelevant in a non-adherent patient. Therapy requires usage, and by increasing comfort and tolerance then long-term adherence may increase.
V̇-Com™ could slightly increase the P90% / P95% in auto-titrating mode at high pressures. For example, with a circuit exhaust of 30 Lpm, V̇-Com™ will decrease the pressure on the patient side of the V̇-Com™ by 0.6 cmH2O between breaths. Therefore, the resulting P90% / P95% recorded by the PAP device may be 0.5 cmH2O higher, but the P90% / P95% experienced by the patient is unchanged.
To further explore the circuit effects, we have tested combining two and even three V̇-Com™ devices in series, which doubles or triples the effect of V̇-Com™, respectively (we are not recommending this for patients). With an exhaust flow of 30 Lpm, two V̇-Com™ devices in series would cause a pressure drop of 1.2 cmH2O (2 x 0.6 cmH2O). However, this pressure drop may not increase the P90% / P95%. For the P90% / P95% to increase, the patient must have events detected in which the PAP device algorithm responds with a pressure increase. During expiration, exhaust flow is mostly patient flow and flow across the V̇-Com™ is minimal with minimal pressure drop. This unique maintenance of EPAP by V̇-Com™ may prevent additional respiratory events and subsequent changes in P90% / P95%.
For patients who have been prescribed a fixed pressure on a PAP device and have a V̇-Com™ device added to the circuit, a clinician may consider increasing the set fixed pressure by the pressure drop of the exhaust flow (found in the package insert of the interface). For example, if the exhaust flow of the patient’s mask is 30 Lpm at the fixed pressure, V̇-Com™ may decrease patient pressure by 0.6 cm H2O between breaths. The clinician may wish to increase the fixed pressure by 0.5-1.0 cm H2O or just observe and follow.
In a trial of 101 patients, we did not find any increase in the residual index with the V̇-Com™ added to the circuit. In addition, residual indexes are well known to be unreliable.
In auto-titrating mode, the small pressure drop created by the V̇-Com™ may increase the P90% / P95% by the same amount and thus, there should be minimal or no change in the residual index. For patients on a fixed pressure PAP, there could be a small increase in residual index, but this can be avoided by increasing the fixed pressure by 0.5-1.0 cm H2O (the pressure drop of the exhaust flow). However, residual indexes are very unreliable and vary even based on the type of interface. In the April 2022 issue of JCSM, Ni and Thomas reported the difference between machine-detected REI and manually scored REI was 10.72+/-8.43 events/hour, which reminds us as clinicians to focus less on PAP device residual indexes and more on patients’ acceptance and response to therapy.
Expiratory pressure reduction algorithms reduce EPAP, and again V̇-Com™ provides comfort without reducing EPAP. Algorithms that reduce EPAP increase the likelihood of causing respiratory events and by lowering exhaust flow increase the risk of rebreathing CO2 at lower pressures.
In addition, viral-bacterial filters create a transient laminar flow and a linear (not parabolic) pressure-flow curve. This would reduce both comfort and EPAP (therapy) compared to V̇-Com™. V̇-Com™ has a specifically determined and constant resistance that clinicians may use to regulate the flow of the PAP circuit for the comfort and safety of their patients, and this resistance is not affected by conditions in and operation of the PAP device.
Finally, a viral-bacterial filter, being uncleanable, would need to be changed often, resulting in exorbitant cost. V̇-Com™ is cleanable and reusable.
Someone who has become very comfortable with the pressures and flows of their PAP therapy without the use of a V̇-Com™ may not enjoy a V̇-Com™ being added to their circuit. The softening of inspiratory flow and pressure by V̇-Com™ will be a change in experience that they may not prefer. This has been the experience of some long-term users who do not want the V̇-Com™ in their circuit. Now there have also been those who did not prefer the V̇-Com™ at their current pressure, but after being re-titrated to a higher pressure, appreciated the comfort of the V̇-Com™ at the higher setting.
V̇-Com™, like training wheels on a bike, was mainly designed for individuals beginning or having difficulty with PAP therapy to get them experiencing the benefits of PAP therapy faster and easier. However, the majority of long-term PAP users we included in our trials chose to leave the V̇-Com™ in their circuit after the trial. They prefered the V̇-Com™ experience. We have also found since the release that most patients starting PAP therapy with the V̇-Com™ are choosing to continue with the V̇-Com™ long term.
PAP circuits are not designed for a larger Vt and higher RR associated with activities or even anxiety. Increased Vt and RR cause two main problems:
a) Increased perception of resistance in the circuit on both inspiration and expiration. This can be particularly true with extra resistance in the mask. b) Increased likelihood of CO2 rebreathing by overloading the exhaust flow.
When first trying PAP therapy many individuals are apprehensive and unknowingly increase both their Vt and RR which makes the experience, even with a V̇-Com™ in the circuit, less desirable. These individuals need to relax and breathe easily as if they are falling asleep to best experience PAP therapy and the comfort of V̇-Com™.
V̇-Com™ affects inspiratory PAP more than expiratory PAP which may decrease pressure support and tidal volume during NIV therapy. V̇-Com™ has not been tested in adaptive servo ventilation and average volume-adjusted pressure support breathing circuits.
A major problem with PAP therapy is that the majority of prescriptions are written for an APAP range of 4 (or 5) cm H2O to 20 cm H2O, yet the average and most common pressure required is 12 cm H2O (This is from a database of >8000 consecutive patients and excluding those patients that required > 20 cm H2O and were prescribed bilevel PAP). Few patients require <7 or >18. During PAP therapy set-up (and demonstration) most patients are tried at 5-6 cm H2O, yet more than half may require 12 or more cm H2O. These patients may have a very difficult experience in the middle of the night and stop therapy.
To improve early acceptance of PAP therapy, which has been shown to increase long-term adherence,5 new patients should experience higher pressure (8-12 cm H2O minimally) during set-up. Have them breathe slow and easy, tightening their chest and abdominal muscles to learn to resist the pressure and control the flow. Once they can accomplish that, then place the V̇-Com™ in the circuit. They will see the ease in breathing the V̇-Com™ immediately adds. The comfort and tolerance they experience with the V̇-Com™ will give them confidence in this critical beginning of therapy, especially in the case that they require higher pressures.
V̇-Com™ will increase early tolerance across a patient population, and early tolerance has been shown to increase long-term adherence.
It is EPAP which forces the flow of expiratory gas out the exhaust system. At low EPAP, peak expiratory flow from the patient may exceed the exhaust flow and rebreathing may occur. At higher pressure settings (higher EPAP), the exhaust flow will exceed the peak expiratory flow and circuit rebreathing will not occur.
V̇-Com™ allows new patients to tolerate higher initial PAP settings while maintaining EPAP and exhaust flow to prevent rebreathing. The invention of V̇-Com™ allows comfort while reducing the risk of rebreathing CO2.
2) Morrell M et al. Retroplatal cross-sectional area preceding an apnea. Am J Respir Crit Care Med 1998;158(8):1974-1981.
3) Gugger M et al. Effect of reduced expiratory pressure on pharyngeal size during nasal positive airway pressure in patients with sleep apnoea; evaluation by continuous computed tomography. Thorax 1992;47(10):809-813.
4) Heinzer R et al. Lung volume and continuous positive airway pressure requirements in obstructive sleep apnea. Am J Respir Crit Care Med 2005;172(4):114-117
5) Budhiraja R et al. Early CPAP use identifies subsequent adherence to CPAP therapy. SLEEP 2007;30(3):320-324
6) Ng JR et al. Choosing an oronasal mask to deliver continuous positive airway pressure may cause more upper airway obstruction or lead to higher continuous positive airway pressure requirements than a nasal mask in some patients: a case series. J Clin Sleep Med 2016;12(9):1227-1232
7) Deshpande S et al. Oronasal masks require a higher pressure than nasal and nasal pillow masks for the treatment of obstructive sleep apnea. J Clin Sleep Med 2016;12(9):1263-1268.
8) Ebben M et al. A randomized controlled trial on the effect of mask choice on residual respiratory events with continuous positive airway pressure treatment. J Clin Sleep Med 2014;15(6):619-624.
9) Ni Y-N, Thomas RJ. A longitudinal study of the accuracy of positive airway pressure therapy machine-detected apnea-hypopnea events. J Clin Sleep Med. 2022;18(4):1121-1134.