Clinical 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.

The answer is no. V̇-Com™ is not a therapy but an accessory to PAP therapy and is only indicated for use in a PAP circuit. To use a V̇-Com™ as indicated, an individual must be on PAP therapy which is a prescribed therapy. No separate prescription for a V̇-Com™ is necessary.

V̇-Com™ provides comfort without compromising therapy. V̇-Com™ attenuates or softens the peak inspiratory flow that is often troublesome to new CPAP patients (and noninvasive ventilation patients). The highest flow rates generated by the PAP device occur during inspiration when the device generates both the exhaust flow and the patient flow (for tidal volume). Flow in a PAP circuit is turbulent, not laminar, and pressure changes by the square of the flow rate. Therefore, V̇-Com™ has its maximum comforting effect during the high inspiratory flows.

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 increases1 and end-expiratory pharyngeal cross-sectional area decreases2 in the breaths preceding a hypopnea or apnea resulting in inspiratory pharyngeal instability.1 EPAP overcomes this phenomenon and maintains pharyngeal patency directly2 from “splinting” of the airway and indirectly from the increased functional residual capacity.4 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 adherence5.

The length of time will vary among patients (Just like training wheels on a bike). Over weeks (or months), patients develop tolerance to the peak flows and pressures of PAP therapy. Once a patient can easily tolerate the peak flows and pressures of PAP therapy, the V̇-Com™ device may be removed from the circuit.

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.

Again, V̇-Com™ is engineered to provide comfort without compromising therapy. V̇-Com™ lowers inspiratory pressure and peak inspiratory flow rate but has minimal to no effect on EPAP. By stabilizing the airway during exhalation with EPAP, inspiratory obstruction can be avoided.2 Hypoglossal nerve stimulators utilize this same principal by beginning stimulation during expiration.

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 Philips Dream Station 2, 17 on React Health 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.6-8

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.5

A single V̇-Com™ in the circuit has little effect on the auto titration, particularly with patients who require lower pressures. With higher pressure settings and higher exhaust flow rates, P90% / P95% pressure may increase slightly, yet we did not find this in a trial of 101 patients. To minimize this possibility, always put V̇-Com™ into the PAP circuit with the PAP device off. Auto-titrating algorithms usually monitor the flow in the system initially to determine a baseline before titrating. If the V̇-Com™ device is already in the circuit when the device turns on, we have not found V̇-Com™ to significantly affect event detection in either Philips, ResMed, or React Health (formerly 3B) devices.

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.9

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 unreliable9 and vary even based on the type of interface.8 In the April 2022 issue of JCSM, Ni and Thomas9 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.

The answer is no. Whether a flow-based or pressure-based algorithm, we have not found V̇-Com™ to affect the operation of expiratory pressure reduction algorithms including C-Flex (and A-Flex) from Philips, EPR from ResMed, Reslex from 3-B Medical, iPR from ResVent, or CC+ mode from Sefam.

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.

Considering the cost of sleep testing (both HSAT and polysomnogram), office visits, the PAP device, interface, and other supplies, the V̇-Com™ device, by increasing comfort, may be the most cost-effective part of treatment. If a patient cannot tolerate the PAP device, all the costs of diagnosis and treatment were a waste of money and time. Also, those patients who fail CPAP therapy will be presented with the much higher cost of an oral appliance or the exorbitant costs of surgery. The V̇-Com™ device is a tremendous value for patients prescribed PAP therapy.

Absolutely not. A viral-bacterial filter creates a variable resistance that changes greatly depending on the moisture content in the filter. If the filter becomes saturated, it could be dangerous by obstructing flow and could lead to marked CO2 rebreathing. Plus, this variable amount of resistance could confuse the auto titrating algorithm.

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.

Soap, water, and a small brush. Specific cleaning instructions are detailed in the package insert. V̇-Com™ is single patient, multi-use device.

In summary, no. Obviously, a set fraction of inspired O(FiO2) delivered from a high flow Osource into the PAP device is unaffected by the presence of V̇-Com™ in the circuit. We tested bleeding O2 at 2 Lpm into a full-face mask and into the circuit between the circuit hose and nasal mask tube with and without the V̇-Com™ in the circuit. In both PAP circuits the FiOincreased by 0.5-1%. This was expected as the inspiratory pressure drop decreases exhaust flow and less Ois lost in the circuit during inspiration. Again, the change is minimal.

The answer is minimal. Because V̇-Com™ has more effect on inspiratory PAP (IPAP) than EPAP, we expected V̇-Com™ to reduce the level of pressure support (PS), where PS = IPAP – EPAP. However, our testing showed little change (< 1-2 cmH2O) in PS (IPAP 20 and EPAP 10) with V̇-Com™ in the circuit. With bilevel PAP the level of PS is usually titrated to a target tidal volume (Vt). To minimize the effect of V̇-Com™ on the target Vt, place V̇-Com™ in the circuit before titrating the level of PS. V̇-Com™ has not yet been tested in adaptive servo ventilation and average volume-adjusted pressure support breathing circuits.

Yes, but not necessarily. V̇-Com™ was indicated for individuals initiating or struggling with PAP therapy. However, we have had many patients acclimated to PAP therapy want to try the V̇-Com™ and subsequently preferred the experience with V̇-Com™. Partly for the softened inspiratory flow, partly for the decreased leak, partly for believing they felt better the following morning with the V̇-Com™, and partly for the decreased noise from the device, many long-term PAP users have chosen to add a V̇-Com™ to their circuit. We were not expecting this prior to launching the V̇-Com™. We have subsequently broadened the indications for use to provide inspiratory comfort to any patient on CPAP, APAP, and bilevel PAP.

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.

You should breathe the same as you do without a V̇-Com™ in your PAP circuit.  No change. However, we find many patients do not understand how to breathe on a PAP circuit in general. When beginning PAP therapy (putting on the mask and turning the PAP device on) you should be lying in bed, relaxed, ready to fall asleep. Your respiratory rate (RR) should be slow, and your breath size (Vt) should be smaller. You should focus on breathing that way. It may help you fall asleep.

PAP circuits are not designed for a larger Vand 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 COrebreathing 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™.

We recommend keeping your V̇-Com™. After cleaning and drying your V̇-Com™ per the instructions, place your V̇-Com™ in its heavy duty, resealable plastic package and store with your PAP equipment/supplies. In the future your PAP therapy (pressure setting) may require changing and your V̇-Com™ device may be required again. If the V̇-Com™ is showing signs of wear, then discard it.

For most patients the answer is yes, but not every patient will require a V̇-Com™. Just like training wheels on a bike. Training wheels would help almost every child ride sooner, but not every child needed them in order to learn to ride.

There is a small subset of patients with COPD, hypoventilation, and even morbid obesity where the higher IPAP is necessary for treatment. If the V̇-Com™ is to be included in the circuit, the clinician must account for the decrease in IPAP > EPAP.

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,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.5

However, V̇-Com™ may actually help prevent rebreathing CO2 by helping patients tolerate higher initial pressure settings which better eliminate CO2 from the PAP circuit. Rebreathing is the phenomenon of inhaling the gas just exhaled by a patient. Exhaled gas has lower O2 (15-16% vs 21% FiO2) and much higher CO2 (5% vs 0.04%).

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. 

1) Tamisier R et al. Expiratory changes in pressure: flow ratio during sleep in patients with sleep-disordered breathing. SLEEP2004:27(2):240-248.

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.

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